Unable to speak to someone to cancel a contract

I have tried to get in touch with MTN on 4 different times & days where I waited on the line for 20 minutes in each instance with no answer from MTN. I want to cancel my contract as it expires at the end of February 2021. I have also been to the Woodmead & Mall of Africa branches and they cannot assist me - they tell me to contact 135 (the number that the retention department NEVER answer). Why do you make it SO difficult to cancel a contract with you?