********** upgrade and exorbitant debit order premium that I didn't consent

A ********** upgrade was done using my account details by a consultant named Sechaba Mothiane and he confirmed that someone called in impersonating me however refused to avail this call to me claiming its company policy. He also denied me access to his manager confirming that the matter is sorted. I then asked him to confirm my next billing but he couldn't confirm stating claiming that he doesn't have access to that information. I spoke to his colleague Martin Benjamin who also promised to look into the matter and revert regarding my next billing but that never transpired. On the 21st of March 2021 i received an sms from my Bank confirming a debit order of R3514 from R628 that went off from my account when i was told by Sechaba that there wont be any escalations in terms of my premiums. I demand that a senior person contact me and resolve this matter as in yesterday. I also demand that MTN i listen to this so called that Sechaba claims it existing and if such call doesnt exist i want to know what steps will be taken against Sechaba