Mtn is ruining my life

Had a 24 months contract with Mtn when it was due for an upgrade i terminated it because I didn’t want an upgrade when I terminated it I had already paid for that month I even asked the person who was helping me if I owe anything else and he said by 8 months down the line when I’m trying to apply for finance I’m being told I owe Mtn and they have handed over to the lawyers I went to Mtn shop in Midlands mall they confirmed that and they can’t help me , when I phoned to asked them which lawyers the lady said it’s being handled by Mtn Legal and I need to wait 5 days for them to get back to me. I just want to clear my name please tell me which lawyers or get your legal department to contact me because this is honestly ruining my life!!!