MTN FAULTY DEBIT ORDERS

I have signed a contract with MTN on 21 May 2020 for the amount of R99 x 24 months. Since my contract started MTN deducted another amount every month, anything from R151 - R171 per month. I have phoned MTN, went to the branch (Keywest) where I took out the contract twice and still no response yet. They even made a copy of my contract as they did not have my original contract anymore. How on earth can a well known company make such mistakes and think they can get away with it? I have recalled all my debit orders since my contract started and I will NOT authorize a debit order from MTN again. This mess needs to be fixed and thereafter I will be paying monthly via EFT.