MTN overcharging clients on contract.

MTN is overcharging my contract fees. I am disputing the monthly billing of my contract. I signed-up for a R204/month contract but currently I am being debited over R1000 per month. I have called MTN several times and they overcharging me from buying data and airtime from a tuck shop or my bank account. They also claiming to be given me 2GB on the 20 May 2020 at 12h00 which is a lie.