Account dispute.

Hello. I'm Bhekizenzo Malambule. Last year August I received a call from Mondo. I was offered a contract that will come out with the router and MTN sim card. Few days later the sim card was delivered to me and not the router. I then call Mondo and made arrangements to cancell the service because I was not happy about the contract. The problem now is that I'm trying to buy myself a car but I can't because my name is in credit bureau because the cancelation was not done. I when called Mondo again 2 weeks back they confirmed that the cancelation request was sent to MTN and they rep**** back confirming the cancellation. So my question is that how come did MTN handed over my account to debt collectors for the service that was cancelled? I have been trying to reach to MTN about the matter but I'm not getting any assistance or positive feedback, both MTN and Mondo are not willing to assist. Please assist me in need my name to be cleared and I also need a written statement from MTN confirming that my name will be cleared.