RMCS stole my mom's phone number!!!!!

My mom had been using her number since the early 2000s. It suddenly stopped working and were told by MTN that RMCS stopped the number. How, and who RMCS is? We don't know. We contacted RMCS via email and gave them a number to call. They called 2 times but the phone rang for 15 & 6 seconds and stopped ringing before I could answer. Tshidi immediately sent an email saying that they tried calling multiple times and there was no answer, he/she did not even ask when is a good time to call. I think the strategy is to deliberately give missed calls so they can pretend they tried and it's the complainant who did bother to answer their phone. I even rep**** their email with a screenshot showing that my phone rang for a few seconds and that I also tried to call them back. My mom is still without her number and this company is not responding.