Outstanding account

Good day I had contract with mtn however things went bad was out of job ,I couldn't pay anymore, it was handed over to MBD I tried to pay and i didn't manage to pay at some point. I got a job and called MBD to inquire about my outstanding balance, i was told the debt is closed on their side therefore it was taken back to MTN i contacted MTN and was told its purged internally , I asked them for a letter that says the account is closed on the 5th of January till this date i haven't received any correspondence , i don't know what to do anymore.