Appalling service from MTN.

I took month on month with MTN Fourways some time back, but the Wi-Fi was always buffering so I decided to cancel it, at that time I was no longer working in Fourways I went to MTN Dobsonville to return the router and cancel the WI-FI since I was now working there. They refused to take the router, and I was told to take it back to Fourways because the deal was not done there I then called the MTN call center for assistance, the call center agent said I must go back to MTN Dobsonville and said I must give them my phone so they can talk to them they still refused. I then cancelled the debit order because I was no longer using their router. Today I just found out that I owe MTN I then called their call center again to find out what is it that I owe for because I have not been using their services for some time only to be told that they have just cancelled my contract today how when I was not using their services what is it that I have been billed for? I was holding for more than 30 minutes only to be told to go back to MTN Dobsonville for what when they refused to take the router in the 1st place. I then asked to speak to her supervisor and my call was cut off. all I want is for them to reverse the charges for all the months that I have not used MTN and cancel the contract.