There's a bit of a back story so please bear with me and I'm trying to keep it short.
2 dc, split 7 yrs ago. There was ea and when I finally got the courage to leave he upped his game.
He tried to take cb of me even though I was main carer resulting in cb stopping and it took 12 months to be reinstated which they did back date.
He then stopped having dc on the days I worked (shift work), thankfully my boss was understanding and I changed my hours to childminder friendly hours.
He refused to pay maintenance and I had to go through CSA.
When childminder was no longer able to have dc my friend temporarily looked after them as I was stuck (he will not have them apart from his scheduled every other weekend) he reported her to Ofsted.
He tried to swindle me out of money from house sale but I had a great solicitor who saw this.
These are the main things he did since splitting there are plenty of other things too.
Anyway back to now, the CSA case has closed and I had to move to CMS. he tried to do a private arrangement but because I do not trust him at all I wanted it done officially. I now know why he did not want me to go through CMS. Turns out they go straight to HRMS for figures and not rely on payslips like CSA used to do. They have now written to him and he has to pay me £127 more a month now than he did for the past 6yrs.
He is not happy and tried to haggle with me, saying he won't be able to take them on holidays etc (I've only managed to take mine abroad twice since split, he goes a couple of times every year usually without dc). He also said it would not benefit him to take them for a week to give me a break 
as he'd still have to pay the same...
I stuck to my guns and told him, I'm now super anxious what he's planning to try and fuck up my life yet again. I'm worried he'll let it out on the kids.
I can so do with the extra money as dc are getting more expensive with age.
I might be worried about nothing and he'll just pay...but he's such a vindictive person he won't just take it.
Don't even know why I'm writing this, guess I need reassurance that I'm doing the right thing for dc. After all he's their parent too and should contribute. Sorry for the essay