Them: The aunt and uncle have been appalling for behaving like this. Immature, selfish and demanding. They are, in fact, the assholes here.
Her: Getting married is stress on steroids and a (I assume) young woman may simply not have the confidence yet to stand up to elder relatives' demands. Sadly she's not able yet to assert herself.
Assuming she did actually want you there in the first place, of course - this may have exposed an issue you might not have realised exists and will become an elephant in the room if your relationship continues.
But the pressure of having to appease mum's family (whom she's known all her life and are tied up with memories of mum) or they don't turn up may have been overwhelming so close to the event.
It's her decision.
Him: Being the father of the bride is HUGE and going along with whatever she decides was his only option. And if she refused to change her mind, that's her choice.
It could impact on his relationship with her and his family if he'd refused to go, or put his foot down and demanded you be included, or simply presents you as a fait accompli plus one on the day.
Where he appears to have been an emotional wet lettuce is in how it seems he's behaved towards you. We weren't there of course but it does seem that he failed to empathise, be understanding, considerate etc towards how you're feeling. My mother's late partner was like that - his life was conducted in a series of boxes and she wasn't included in them all.
That for me is the issue.
You: Being sullen, resentful, silent treatment, snotty messages, turning phone off, getting wound up, having a row isn't the answer.
So wish the bride a happy day, send congratulations to the groom and plan a nice you-day.
Leave your phone on - see if your DP bothers to keep in contact.
Compose a careful, calm and civilised conversation with him when you next meet over exactly how this has made you feel. Tell him it's important in any relationship that both can express how they feel and how the others behaviour has affected them. Hard, but stay cool and relaxed so he doesn't have anything to react to. And observe his behaviour and response.
Because this is going to be a trailer for exactly how your life (and your position in his) will be together.