Bad service/ forced to pay for services that i did not apply for

I had a contract with mtn south Africa which ended on 31st of August 2021 on the 2nd of August i sent them an email stating that i do not want to continue with contact and that they should change my number to prepaid but instead they sent me a message that i will be paying for the services which is not what i want. Their agent called me about the upgrade and that i dont want to pay for any services the agent was rude and he did not even transfer to cancelation department instead he said i should call 135 and he hungged up. I called 135 and followed their options of cancelation and i hold on for 1 1/2 hour until i hanghed up the phone without assistance. Im very disappointed with the service that i got from mtn.