I cannot shake off the CSA after 16years!

Hi I'm writing having seen the Oneshow report, only today I have written to my MP out of despair, as I cannot shake off the CSA after 16years! I have made a full and final offer to the CSA after a mistake made by them 16 years ago costing me dearly! the offer was made on the 7th October and accepted by theaccounts manager who advised me to cancel the direct debit in risk of predijucing my offer which I did. Only to be called this week demanding full and final settlement by the end of October by their Debt enforcement dept. is this legal and where do I turn?

Anon