Unsubstantiated debt collection

by Bridgette
(Antioch, CA)

I am currently and continue to be harassed by a debt collection agency for an alleged unpaid account for XM Radio. I received a bill from XM Ratio notifying me of an increase due to an added broadcasting fee. On that day I wrote and signed this letter stating I did not want to continue my service and pay a higher fee and requested my service be canceled. They have turned this account over to EOS CCA collection agency, whom I also sent a copy of my written cancellation and as of today they continue to harass me and continue to ruin my credit. How do I resolve this?