Ex rejected direct payments once she lied to CSA

Ive got a child with a ex.and was giving her money till i had open heart surgery then.lost my job my house everything.then my ex told csa i neva given anything to her and now ive got to pay £3500 back date.now she found out im going back to work and i said ill give u £25 aweek she said no and took me to csa cuz the more money i earn she gets more for example if i earn £300 before tax i have to pay £36 aweek.even i got kids living with me but if i earn £600 aweek before tax then got to pay £62.but my ex got 3other kids a partner that works.

but ive got to pay £100 rent gas eletric water council tax kids football dancing hospital as my little 1 got problems due to being 13weeks early.for example.£600 take tax leaves me £480 aweek take bills = £100 rent eletric £30 aweek.gas £30 water £15 council tax £30 van insurance £25 petrol £50 plus £5 footy for my son footy and £5 aweek dancing my daughter  that leaves me with £180 and still got to get kids to scholl food dinners and days out if they be good.but csa dont see that.if there was no csa and told the mother to deal with the father then there would be 100% fathers who can see there kids and buy there kids stuff not pay for the mothers luxury life.if the father has to pay the mother then the mother should lose that amount out of there benefits.and i bet u the mother wouldnt go csa cuz there will lose there benfits money.