MTN and Mondo you FRUSTRATE ME!

Good people i need help. I do not know how to communicate this anymore. I got an MTN iphone 7 contract last year December from Mondo. The phone was faulty and i returned it the same week i received it (Within the seven days to MTN in Rosebank. They failed to return the phone I then CANCELLED IT. Theres been back forth communication between Mondo (Rewardsco) regarding this cancellation but no one is giving a document that shows it has been cancelled. GOSH! Its taking to damn long! Now i am being threatned by MTN lawyers because they handed me over, for A FREAKING PHONE THAT IS SITTING WITH THEM. GUYS! AGAIN! STAY AWAY FROM MTN AND MONDO, They run away from responding and to me. I am really sick and tired and regret ever engaging with MTN an Mondo!