SWOPING A GRANNY'S ACTIVE NUMBER TO NEW USER

My Mother is a 72 years old who is staying alone in hammaskraal and we call her everyday and buy her airtime to our surprise this morning someone answers her cellphone number. We were so anxious thinking the worst might have happened.The person is telling me he bought a sim card thats the number he was given. He is not even ashamed to tell me he needs R100 to go cancel the number for his efforts.My Mother has been using this line for over 5years and now VODACOM does something like this and i called customer service & i am told it has never happend before.Now my Mum must buy a new sim & i must forget about RICA as it is inmaterial.This is absurd, how do you swop a number that is everyday functioning?I am so deeply hurt and it is a bad service from vodacom