maintenance or mortgage payments, not both?

Hi all,
just wondering if you could share your views.
My stbx of 9mths has continued to pay half of all mortgage payments. Initially I was happy to manage until i reduced my hours for childminding reasons, with my reduced income i was not in a position to pay for usual swimming lessons etc. So asked the kids dad for £30, for half of fee, it was the first time i had to ask and he refused saying he couldn't afford it.
He is adamant that he pays enough.

I have told him i am applying to the CSA to prove to him that he isn't paying enough. I do not intend to pursue maintenance through CSA, just want him to see proof in black + white. Besides, he says if CSA make him pay he will then stop paying his share of mortgage payments.

Another gripe I have is that tonight when he dropped kids off, my oldest has returned with another pair of best jeans ruined. What do i do?? I asked him, as he is yet to buy son birthday present of 1 mth ago, if he would provide money for new jeans. I knew the answer, but felt i had to ask.
I don't want to send good clothes anymore cos i can't afford to replace them, but its not fair on our kids, if i send round Dunnes jeans then it wouldn't bother me so much. Or, I could ask him to provide clothing for kids while they stay at his?? What do you guys and girls think?

Catty