Mtn contract cancelation problems

My Father in law has 4 contracts with mtn, 2 of them was due for upgrade but decided to cancel the 2 contracts but keep the numbers as prepaid. So on the 27/11/2020 he called 135 customer care to cancel the contracts and find out the amount due. The lady at mtn customer care canceled the contracts and said there was no amount due and gave him a cancellation ref. Nr: ***. As of 14/12/2020 all 4 numbers was suspended. So on the 15/12/2020 my father in law called mtn customer care to find out the reason for the suspension of the contracts. The person at mtn customer care said that there was a amount of R629 outstanding on the 2 contracts that was supposedly canceled , he told them that he had canceled the contracts on the 27/11/2020 and that there was no amount due, the mtn customer care person rep**** "SORRY WE MADE A MISTAKE " and that he has to pay the amount due and wait 2 days and call customer care to cancel the contracts again. I feel that my father in law nor anyone else has to pay for mtn's mistakes, i am truly disappointed in mtn.