MTN is *********!!!!!!!!

Is MTN becoming Telkom? Are we no longer allowed to cancel MTN contracts? My Mtn contract expired on the 26th May 2023, i was then advised by MTN customer services to call on the 26th May and convert my line to prepaid. I did just that and spoke to Jonathan but to my surprise on the 27th i got allocations which meant i will be billed R140 and that my line would be cancelled in June because of a waiting period (weird since my contract expired). Today i woke up to a R640 bill from MTN for this expired contract. Somebody please help me because i have called mtn numerous times and they assured me that this will not happen. I do not want another contract as i cannot afford it but you refusing to cancel this is just *********.