FRUSTRATED ABOUT THE HARASSMENT!

I had 2 arrear accounts at Norton Lambrianos Attorneys, which I paid off. The next moment I got sms's from DMC to say that my account has been handed over to them for collection and I must now make arrangements with the to pay it off. So I phoned the number provided in the sms and told the agent my story. She gave me an email address and asked that I send the proof of payment and the paid up letter from Norton Lambrianos Attorneys to them, which I did. I have ever since still been harassed daily with agents calling me about my outstanding account and receive sms's daily to the same regard. I have been phoning the call centre multiple times now to try to sort this matter, but to no avail. The is no supervisor or manager also available to talk to. I have left my number as well for a manager to call me back, which has never happened! I am beyond the point of trying to solve this matter and speaker to every other agent who claims to be able to assist me, but never does.