MTN account I don't have

I am harassed by lawyers calls because of a phone I never owned!I have tried to explain what happened between MTN and myself and also wrote affidavit that I returned the phone immediately because it could not be Ricard and was not activated,I returned it and they took it back!but still they debited money from my account,I tried to complain to the Agent many times but still money was debited!afterwards I was called by rude agents telling me they are from lawyers and my account was handed over of-which I don't have any MTN acc today!!also I received an SMS saying I am owing R9 920,32 in an MTN account for what???whose account am I suppose to pay?no no no!!this is too much