Vodacom disconnected my sim for no reason

My brother bought a Vodacom Sim card at a Vodacom store and had the sim card Rica'd at that store. He has been using that Vodacom number for +/-3 years, then suddenly the number stopped working, he went to Vodacom Bridge City Mall 3 times and they were offline. He has been without service for over 5months and Vodacom has given the number to someone else. How can Vodacom take that number and assign it to someone else when it is registered with his ID number. That cellphone number has been used for job and school application, even for banking account. How come Vodacom switched the number to be used by someone else. How safe is it to use this service provider for such a thing to happen. I want my number reactivated!