FNB Connect Voice calling issues

I switched to FNB connect a few months ago without issues. However , for the last 2 months I can not receive calls on my phone..Someone will call me and I will be able to hear the person on the other side, but they can not hear me. When I call them back, no problem, then everything is clear and workig. This forces me to call back the other person on my account. I did call customer care, but did not help. I know FNB connect ***gy back on the Cell C network, so I am not sure who to complain to.