Incorrect billing, migrated to pay as you go

I am at a complete loss for words. MTN still sends me messages that I owe them money. It does not help to phone head office, they tell me I must phone 135 which is also fruitless and a waste of time. I cancelled my contract in June 2022 - which is the date MTN gave me I must send my cancellation by email. The email was received that I will be migrated to pay as you go.

All of a sudden, I am being told that I never cancelled my contract. This is really creating a lot of stress for me and this is lying on my credit record. My emails are not getting answered. I use to think MTN is the best cellular service provider, but I changed my mind. I am going to take the matter up with my lawyer as I am not getting any response or phone call from MTN. Please stay away from this service provider. Or should I say non-service provider.