Telkom mobile is recycling used phone numbers

Telkom mobile sold my MTN number to someone else on a prepaid Sim card. This other person has now been trying to log into WhatsApp using my number and telkom says there's nothing they can do about it. I got a call today from someone trying to reach their sister on her new phone number which turns out to by my exact number. How can they possibly not be able to fix this? is this some inside job to bypass the Rica system?