Hi Jennifer,
You need to take a direct approach with CTC. First send them letters revoking their infamous "Wage Assignment" ASAP! Then send letters stating your proposal to pay principal ONLY, also send C&D letters as well. Make sure to send all letters certified with return receipt. You can also fax and email them these same letters.
Do not communicate with them telephonically, they can be quite nasty after they figure out your gameplan

So try and keep communication documented if you can. They are ILLEGAL and based out of Malta, so you have the upperhand with them. They are not licensed anywhere in the US.
I dealt with them only through email and USPS. They settled with me for principal after they had no means of collecting otherwise(wage assignment). Stay strong and firm with and make your intentions clear. Best of Luck :P
P.S.
Please ensure that your bank account is closed or you have a hard debit block on your account. They will try to debit it any means necessary.