MTN contract hell

I walked into MTN on June 2022, and purchased a new phone on contract as I was due for an upgrade little did I know it will ruin my credit!!. I was in a rush so I told the lady at Mtn bridge city, she had my details, she can put it on a new number which I had been using as non contract, since I had one number already. She did the worst thing you can do, which was not to listen to me as I speak. She wrote the wrong number at the end my number ends with 79 she wrote 78. Which was an existing Mtn number registered to unknown user, who ended up getting on a Mtn new contract without her knowledge, two days later I wonder why I'm not getting welcome messages to say I just took new contract. Instead I got an email confirming that I got new contract, which was strange but I didn't think it was because of the wrong details she put, on the third day I call MTN bridge city, I tell her I don't have the minute they promised me plus the data I should be getting. She then realised the mistake she made, and meanwhile the person recieving the data has no idea this data and airtime is not free, she uses it, unsuspectingly thinking this is some kind of promotion from MTN,she used over 1.6gb and bought more data which I was later told cost me R1600 to R2400. A purchase I had not made and was done in someone else's number under my contract 😭!! How do you make a customer pay for something that was a clear mistake from staff, and you make me pay??? I refused to pay extra for some time so that Mtn can fix this mess, I called AI emailed I went to head office at umhlanga, nothing was done instead I was charged more for someone else's mistake, today Mtn out me in credit bureau for non payments! Please help me