Very bad service

I bought a phone from this shop in Harrismith then after 3mnth it's stopped working I took it back .they booked my phone with MTN apparently they send it back to the shop cause the EMI of the phone doesn't correspond with the one on the box .it's almost 3 months now my phone it's still with them Nd I'm not getting any response from the shop,I wrote to the customers service BT no response until so far .TFG should treat their customers with care Nd teach shop managers respect .all I want it's a new phone or a refund