Bad service, no help from MTN I am not their customer- but they got their commission

Since buying a dual sim A2 core phone in 11/20 with locked MTN sim even tho I am a Cell C customer I receive calls day and night regarding debts I am not responsible for as MTN recycle their no's after 3 months - the same with SMS messages received from lawyers or folk trying to get hold of Lorraine Steenkamp in Kimberley or Pinkie whomever and wherever she resides - MTN does not respond and if I ask for a refno none received - I need my life back plse