MTN is forcing me to stay on their contract for 3 years

I requested MTN to canceled my contract 2023 September. The reason for cancelation is that I switch to another service provider, and I requested them to close this account. I never used there package after. 2024 I got a call from one of there debt collection department saying my account is owing and I asked her to verify the cancelation. I never got any updates after until yesterday when someone call to be coming from a third party legal collection saying my account was handed over to them. MTN is struggling on business and its forcing me to stay on there contract even if multiple times I requested to close it.