Unsympathetic CSA kept me in the dark

My ex wife decided to leave the CSA and for us to make our own arrangements and we agreed a suitable figure that I have paid since via direct debit.

Unknown to me, in Oct 2012 my ex wife returned to the Csa and asked to go onto their system as a case again. The Csa informed me of this in February 2015 (two and a half years later) and now state that I owe arears from Oct 2012 to the presnt day calculated from the difference between what I was paying and what the CSA calculate I should pay.

This amounts to thousands of pounds and it would have been impossible for me to know that this had happened and that I was in arrears. The CSA have been completely unsympathaetic to this situation.