I don't owe MTN anything

Will you please assist me. I got a call 2019 from MTN and they said I owe a contract phone of the amount R29000. I have never used MTN in my life and would never purchase or take a phone of that amount. No one is giving me an explanation of anything. They're just saying I owe them R29000 for a contract phone. They have also tarnished my name on the credit bureau and now the matter has been also handed over to the lawyers. Please help me on this regard.