MTN contract

I took an iPhone 13 with contract from MTN on September and they told me that I will pay month end of October the amount is R530 per month okay month end I paid R682 cause I was charged out of bundles rates since I can’t buy data it’s a prepaid SIM card so I bought data from my MTN account I didn’t have a problem with that This month when I check my bill it says R1450 how did my bill get so high whilst I have to pay the R530 for the phone and I also bought data that cost R270 from my MTN account this month so why are they charging me that kind of an amount I sent them an email even now they didn’t respond