CSA do not care about my children, only their money

I was paying for my children and paying the mortgage then my ex took me to CSA.

when the CSA got in touch they said there was arrears from years ago so i was paying £250 a week this was year 2008 and then last year my payment dropped so i assumed that i had paid arrears off and my eldest had left school so left it at that. Then this week i went to the bank to find they had took £430 out of my wage, when i rang they said there had been a technical fault on there behalf and that i wasnt paying enough last year so im now in arrears again, they said if i pay £400 next week they will knock 30% off the arrears taking my future payment from £450 to £170 a week.

I cant afford my mortgage and now me and my second family are looking at repossesion. I cant believe they can do this to people i have all wys provided for my children and all ways will but this is ridiculas dont no what the future hold for me and my second family now but they say it dosnt concern them, Lee