7 months to pass a credit note

I took a contract is January and was not satisfied with the device so within my 7 days period and returned the phone to MTN northgate. It is now 7 months later and I keep getting billed for the phone and my current number keeps getting suspended due to a device or sim I have never used! The credit note had still not been passed and no one can help me. I called mtn weekly, I drive to the store every single time this happens because even the call center cannot help me. Mtn calls me to make payment arrangements which I stick to yet they still suspend my line! Mtn complaints is yet to get back to me numerous emails later. I won’t be reimbursed for my time away from work or petrol used to follow up on a credit note that takes 7 months to pass. How is the internal lack of process a consumers problem?