No paid up letter after a month of waiting

The debt collectors called me saying my MTN account has been handed over and I needed to settle R960. I made an arrangement to settle the account and it’s been settled but to my surprise I still owe MTN an amount of R1200. I phoned MTN to ask them about this and MNT doesn’t know anything about my account being handed to Shapiro and on their system I am still owing. I’ve been trying to contact Shapiro but their phones are always busy, I then sent a text on the 16th of September on their WhatsApp number enquiring about my paid up letter and they said they will investigate and get back to me. I sent a follow up text again on the 20th and they said they’re still waiting on MTN to advise. On the 1st of October I followed up again and they are still waiting on MTN to advise. Today i sent another email and no response. I am furious as these people have black listed me and now my name has a red flag and no one is taking accountability for this, while they have my money