MTN refusing to cancel contract. Taken from pillar to post

I informed MTN of my intention to cancel a data contract I had taken with them since I was struggling with sufficient coverage. I called the coverage department who informed me to go the nearest MTN shop to return the 5G router. I took it to Brooklyn Mall MTN shop and they refused to take the router. I went to Menlyn Mall MTN shop and they refused as well indicating that I need a coverage later to return the router. I called the Coverage department for the letter and the promised to issue one to me. After several days I did follow up and the Coverage department said it was the wrong procedure I need to fill in a document first. I duly comp**** and send the filled document to them. The Coverage department hasn't provided any feedback since 03 March 2025. I contacted the Customer care department who referred me back to the Coverage department. Since 25 February MTN have been taking me from pillar to post. Their service is quite pathetic