MTN Bad service

I'm extremely disappointed with the service I received from MTN. I returned my router and asked to cancel my contract because of poor connection I always complained about , but the process has been a nightmare, took it to the store. The store gave me a ref number and told me to call customer care, who then said the store should've cancelled it. When I went back to the store, they said it wasn't their responsibility. Now I'm still getting invoices and having money deducted despite returning the router. This lack of clarity and communication is unacceptable. I hope you can look into this and resolve the issue ASAP