MTN billing mistake

My MTN contract ended on the 13th of November. I use it for internet and the cost is R469 a month but on the 11th of November it said on the mobile app the R4960 was outstanding which is complete hogwash. So I phoned customer care and they agreed it was a mistake but it will take 5 days to rectify. When I tried to upgrade my contract it failed because of this billing mistake and now I'm out of contract and still waiting for them to fix the bill.