CSA says I owe arrears but I cannot afford to pay it

I have just received a letter from the CSA informing me that I owe arrears of nearly £4000.00. No explanation of how I have accrued this as I have never missed a payment for the dates they they have dentified. The payment is taken directly from my salary which suits me as I dont have to calculate it in my monthly budget. the CSA has now added a further £250.00 per month to my payment to offset the arrears without asking me whether or not I can afford it.

I have never refused or contested my payments and was never an absent father…I was living with the children’s mother when an attachment to earning was made! she was unemployed and on benefits. You know what the worst thing is? since I met a new partner she will not even allow me to see the kids and I have had to apply for a contact order. I will have to give up work and go on the dole because i simply cannot afford this arrears which i cannot understand.