MTN is busy collecting my money but i don't have any of their good products and services

I have upgraded my contract with MTN on August 2016 and I got a tablet and a smartphone which the tablet was not switching on I returned it, after few months they gave me another one which last for 3 months then it went off too I returned it and got another one after months, then it went off again just like the other once then I have returned it, the other smart phone I lost it and I have returned the tablet for the 3rd time on the 5th of June I tried to trace for my phone, called the customer service and its 3 weeks now no one seems to know where is my tablet but I still pay for the phones. can you please help with MTN service it is poor and they don't have sense of emergency.