Credit Report: MTN - 'exceeded credit limit' but I have no contract with them

On my credit report I see I have 'exceeded credit limit' with MTN - I have not had a contract with them for two years - since 2018. I then called the call centre who tells me they cannot access my profile/ account because its been handed over to the legal team - 'we will need to log a request because your account is prepaid but handed over to the legal team', I'm given a reference number and I need to call back in 72 hours to follow up. They cannot call me with the feedback as 'they only take incoming calls not outgoing calls.'. Ref ***

I have NO email, NO sms, NO call asking me to pay any outstanding amount - the first I hear of this is with a negative impact on my credit score/ report? I was on contract where the amount was debited monthly - how then am I at fault for not paying when the final amount should have been debited on the end date? Why do I have to contact them after 2 years? Because I see it for the first time on my credit record? Why have they NEVER ONCE made contact with me. This sounds like plain *****.