To tell her it's not her business

[R2G]

Ex didnt pay child maintenance for several years when we divorced.
I eventually went to the CSA.
We both now have new partners. I have had to communicate my childcare arrangements via her for several years - at his ExP request. Every arrangement made this year has been rearranged time wise or cancelled.
He has now had a letter about the new CSA as have I. I plan to pay the £20 to them for then to calculate his payment, but then he pays it me direct. However, if he defaults it is a legally binding arrangement rather than our own private arrangement.
She texted me to ask me to speak with him today. I had already told her months ago that it was a very emotive topic and therefore I did not want to discuss money at all with her/ him and would always go through another agency (I could have gone on to say why, him not paying, his family telling me to starve and then I'd come running back, him holding ten pounds up and telling me to say please, him refusing to come to his sons party unless I paid his petrol etc, me being awarded a small amount at first by csa after several years of nothing and him laughing not to spend it all at once). I didn't go into that just said I don't want to discuss money with her. Him.
Anyway, she has then texted me her opinion that I need to grow up, I should make it direct with him and there would be no issue, I'm wasting public resource etc.
I texted her that it was actually nothing to do with her so I didn't need her thoughts on the topic - she feels it is as it is their family money and so she can say what she wants.
She has now blocked me and my ex has sent a message basically telling me how upset she is, how all she's tried to do is help, how she and her son give up a day a month with him while he sees my son and I needed to respect that's a big ask and be grateful.
AIBU to tell her it was nothing to do with her and I didn't want her opinion on my financial arrangement after telling her many times I would use CSA rather than negotiate a direct arrangement with them.

Thanks Toasty x

OP, you can't reason with the unreasonable. Just because your ex and his current partner keep saying they are right doesn't make it so. Claim through official channels + blocking them on social media/phone + setting up a separate email/bank account = stress and drama free life.

Don't worry, OP. They don't have to think THEY are RIGHT, they only have to convince YOU that they're right. That way, they get to control you, like a puppet on a string. They're dicks.

Well put poverty I'll remember that one. I've wanted to set up an email account for a long time but I've been trying to communicate with him then her for DS sake. I don't want to give them any excuse to say it's 'too difficult'

But, if he can't be bothered, he can't be bothered - not that you should put it like that to ds. Your ex is an adult, who ought to want to see his son. You can't make him, and you shouldn't be making all of the effort.
Let him show his true colours - he might step up and sort himself out.
If he doesn't, it might be better to let it run its course. It will be a difficult time, but at least you won't have to engage with all of the game-playing that seems to be going in now.
My experience is that children will eventually work out who values them and wants the best for them.