MTN bad service ******* 😡😡😡

I app**** for the 5G LTE router last year and returned the unit to South gate branch within 7 days of receiving it as it did give me the service that was offered to me telephonically . Nearly a year down the line MTN is still billing me for the service which I didn't receive and unit returned. When I query with the store they say the department that they booked the unit in with may not have done so and I should have canceled the service telephonically. I did cancel telephonically as this is how I got the advice to return the unit to a branch as it was originally delivered by courier. I want a refund for all the months that my account was debited.