Unacceptable debit order

I honestly don’t understand why should I apply for an upgrade on mtn online and when I have to query I am then referred to third parties who don’t even answer the phone. I did my upgrade online on the 27 July 2021, I took the home 120gb package, which when I realised that it is no what I wanted, I phone to cancel and do a normal data contract that I can use anywere. My contract with mtn was R199 and I was upgraded to R199 again for a 50gb package. A debit order of R1140 came off my account on the 25th of August. I don’t know why must I pay so much. I tried to phone *** but there’s no answer. I have reversed the debit order and I will only pay when my issue is resolved. And I am not going to pay R1000 I want a credit note.