MTN Account issues - pathetic support

I have taken out a mtn Top up sky contract just over a month ago at MTN mall of africa. It was a sim only deal. Contract monthly amount R1019. I was asked to make an upfront payment of R10056 for a sim only deal. I made this payment. My first billing took place today 26/06/2020 and i was debited from my bank account R1610. I assume that this was pro rata plus the new month. The problem is this value should have been debited from the R10056 upfront payment that i made towards the account and not from my bank account. To top it all my statement says im in Arrears of 30 days to the value of 11666. This value is a combination of the R10056 UPFRONT payment i made plus the R1610 that was debited from my bank account. I called the mtn call centre and was told they cannot help me! I need this rectified asap and it must not have implications on my credit rating. This is absolutely pathetic service i should have never re-taken a contract rather went to a service provider that knows whats going on!!! Please contact me to resolve this as no one seems to be able to help.