who do i turn to

So my headset was approved for replacement at mtn repair centre an i was told to collect one at any mtn store.i have been sent to 8 different mtn stores and even back to the repair centre not one of them have stock apparently nobody in cape town has which is very strange cos all the stores ive been to has that phone on promotion.i find this real sad as ive been with mtn for 17years an i never thought of another service provider but now i think its time to move on.so the next step will be to block their debit order until somone takes me serious