Bad service from MTN

I have upgraded my phone account on 21/03/2020 when I was in the store they explained that I have to pay a migration fee of R1008.00. Wich I was in agreement. But when my first invoice there after arrived I noticed that they have charged me the R1008.00 migration fee and then another R9000.00 migration fee. I have then requested that they pls check my account as it is not what was agreed. The request are then opened and a day later closed with no feedback given to me In the mean time they have reported me to credit burrow that my account is not paid up and to date I have been asking them to plse review my account and remove the R9000.00 incorrectly charge and I will pay the outstanding account. I am anable to get hold of any management person to talk to me to have this sorted out and this is affecting my credit record