Unfair billing and unclear process

I took R295 contract with Mtn online then the router was delivered at my address and I wanted to use it at a different address. So that became a problem to a point when I call regarding the issue I was told in that area there is no signal coverage, and I was advised to return it to apply for another one using the address where I will be using it from. I did return it at Heidelberg mall and got IRMS number ‪***‬. But I was double debited because it wasn't canceled on the system, while trying to fix that the agent I angaged with over the phone. He told me I should make the payment but I will be refunded as soon as the other router is canceled. 14 days later when I tried to make the payment using the link I was surprised that I owe R8753 rands instead of the R601 that was meant to rectify the whole mistake. When I called 135 again I was told my account has been handed over to some debt collectors and the number I was given to contact them it ring unanswered. Now I keep getting SMS regarding the amount I have to pay, now it's R9279. 2, mind you the first Router was never used, it was returned due to address and coverage issues and the second router it was used for one month. Please get back to me. Regards Thokozani Zulu