Disgusting customer service

I'm really disgusted by Mtn ,especially considering that it is a proudly South African company and international one Nogal,.I've been a loyal, paying customer all these years,without default and I'm currently paying for a samsung galaxy tablet that has switched of and has become an ornament. It's frustrating because I was using it for work. I have complained on several different occasions about this product. The software has been repaired three times but it keeps switching of. I was promised that I would get feedback in 5 working days, it has been 10 if not longer. I have also phoned the customer service number on numerous times but nobody is picking up (lol) what an irony for advanced telecommunications. I hv told them they must either stop the contract or give me another product, still waiting. Disgruntled and fed up.