TLDR: OP had never done anything like this before, and in my opinion she sadly set herself up for a great fall, although on the up-side if she's as passionate about her subject as she says, then she should take comfort in knowing her words were of great use in helping to promote said subject. Also, I don't think those one here who have disagreed with her have been particularly harsh.
NC for this, and my goodness there's a lot to unpack (most of which I won't). It's interesting though, that those who are replying to explain to OP about how all this works and offering reasons as to why whatever happened did so as it did are being told (collectively, that is) that OP is being given a hard time. I don't agree - it may not be what she wants to hear, but it is all consistent with my experiences with the television and other media work I've done.
I have to suggest that if the OP wasn't doing this for her own benefit of having a few seconds of fame on TV (and there is absolutely nothing at all wrong with that), then it must have been for the greater good of raising the profile of the subject that she is clearly quite passionate about...in which case the "job's a good 'un" in as much as the information she wished to put out there was still used, albeit not delivered by her. At least the whole thing didn't end up on the cutting room floor, so to speak.
I don't have a lot of talent, and I don't have a lot of knowledge either, but I am exceptionally knowledgeable and time-served in one particular subject, and I have been told repeatedly I am a "natural" when speaking on that subject. As a result of this, I've had several television appearances, one of which I was a main contributor to the program, and numerous interviews for radio and written media.
I knew well in advance of appearing on TV that the opportunity was likely to arise at some point in the future, based on the work I was doing, and that it would be a matter of time & opportunity. Ahead of that, I did a lot of research into what makes someone a good guest speaker on TV & radio, and it was suggested that becoming a regular caller on a local radio was always a good start, so I pursued this with my county's BBC radio station - it didn't take long for them to start calling me up out of the blue, asking my thoughts on all sorts of subjects and asking if I'd be willing to go on air "for a chat".
From there I got the chance to appear in a TV documentary. There was no payment for this, so like with the OP, one does it to meet one's own agenda. I wanted the chance to find out how it all worked, what was expected, and what the rules were. I did not contribute to the documentary per-se, rather my contribution was for an interlude to break up the weight of a 50-minute long 4-part documentary, with footage of me driving my car (filmed from inside and out) whilst commenting on the condition of a stretch of motorway was used (along with a great many other people's contributions) between the main features of the documentary.
As others have said, there are rules to be followed, papers to be signed, and objectives to be met. There was no misunderstanding on my part that all of what I contributed to may never be used, and that it could easily be chopped & edited out of context, and so on. The only thing I hadn't bargained on was how long, tedious, and at times boring the whole process could be.
I later got the chance to appear on a local ITV news feature, as the organisation I was heading up at that time had sponsored a charity, and we were asked to contribute. Again, there was no payment, but it was a brilliant opportunity to get the name of the organisation out there for free. This was exactly the same with the printed media too - there was a lot of that at one point. Sometimes I'd be interviewed over the phone and my words used in an article written by the journalist, other times I would be asked to write my answers and send them in for consideration...and it turned out I was a natural at that too, as very often what was used (this always being a minuscule amount when compared to the quantity I had been asked to provide) would be used word for word as I'd written it.
And then later still came the paid TV work...for that I very much did it for the money and nothing else. Hours and hours of answering the same question and doing the same action over and over again so that it can be filmed from various angles does get boring after a while...one appearance saw me away from home for over twelve hours door-to-door; fortunately the fee I negotiated was more than enough to cover all of my time and expenses, but it was a very long day and all to produce a clip that lasted less than five minutes.
In the program where I was a main contributor, I had to devote two days of my life to travelling and filming, and devising a range of activities for the participants of the show to undertake...again, I was paid enough to make it worth it, but we're only talking a few hundred pounds for a hell of a lot of work. Again, it was repetitive and boring at times (so much time is spent just standing about waiting for producers and camera operators to be ready to film), and of the many hours of filming, only about 15 minutes of it was used in the program, but that's just how it is - TV companies seem to want huge quantities of "stuff" so that they've plenty to work with for when the format of the show is eventually decided and footage edited accordingly.
I could get upset about the money I'd spent on resources to make the various demonstrations and activities happen, only to discover that much of it was never broadcast, but what would be the point? I'd included the costs in my negotiations over the fee, so like in any job, you're paid to do it and so long as you do it properly then it's of no concern to us what happens with it next. But without knowing what the OP's motivation was for taking part in this TV article she speaks of, it's very hard to say whether or not she's been treated badly.