Unsettled balace with MTN

On the 22nd of January 2021 I went to an MTN store at Vaal Mall and started a mi-fi contract which was supposed to last for 24 months, the amount I was supposed to pay was R330 per month. On the 22nd of February 2021 they tried deducting R9 500 from my account but failed because the amount I had was below R9 500 so they returned the money they took. According to MTN I owe R9 500 even though I used it for one month and I don't understand why and I have went to the shop multiple times and they've said the reason is because I used "out of bundle rates" therefore I need to pay the amount.I stopped using the mi-fi on the 25th Ferbuary 21.The agreement was that if I had finished the data I had to load data myself and that it would not go to out of bundle rates. The amount has now accumulated to R10 000 and I have received a message saying if I don't pay I'll be reported to credit bureau.

My reference with MTN is BA***