Terrible service from MTN and Mobilesplus

Mtn has been billing me for a cellphone device that I have not received. I have queried this on numerous times with both MTN and Mobilesplus. Every time I call MTN, I get referred to Mobilesplus but I have been billed by MTN. Mobilesplus promises to deal and refund but state that they are waiting for billing info from MTN. This has been going on for the past 2 years.