I am being hounded by phone calls from the CSA.

I am being hounded by phone calls from the CSA.  They were requested to make all communications in writing, at the outset several years ago and more recently, at the beginning of this year they gave an assurance to my MP that they would respect my rights to receive all communications from them by post.  Does anyone else have this problem?  Do you have any advice?  My ex is a civil servant and I feel there's an abuse of power being perpetrated.