My mothers number hacked by ********* and using her number to send whatsapp messages to her contacts

I am writing on behalf of my mother. Her number is used by ********* to send whatsapp messages asking for money. Her contacts are receiving these whatsapp messages and some fall for this trick. We contacted mtn on 083 135 and they seem clueless on how to assist us some saying we must not use the number for 3 months and it will then be closed. who waits for 3 months when the issue is active? if you can please assist us and advise how you are protecting your customers from these *********.