MTN cannot make calls

I have now been battling for more than a week with a new MTN phone that cannot make calls. I have even had a sim swap done. Been to local branch 5 times, call the 135 number many times ( they don't answer most of the time) Call barring is off. The Branch has tried assisting , opened tickets etc but to no avail. This is so frustrating. I am paying a contract ( been using the number for many years) and nobody seems to know how to fix this. Very bad service