Allocated Vodacom Contract Cell number Nightmare

I took out a cell phone contract for my 14 year old daughter through CelluCity in August 2015. I was given a Vodacom cell phone number for the contract. My daughter started receiving phone calls from unknown people. A person by the name of Mervin allegedly a businessman started sending her messages via whatsapp begging her to give up the cell number. Mervin also spoke telephonically to myself stating that the cell number belonged to him and that my daughter will receive numerous calls from his acquaintances. I contacted the Vodacom call centre on 01/09/2015 and was informed that the number cannot be swopped. I was informed that Vodacom after a period of time if the number is not utilized, gives the number away to new customers. The call centre agent Andile advised I must contact Mervin and ask him to contact Vodacom in order for them to explain that his number was allocated to someone else. I want my contract number to be changed and Vodacom refuses. It is sad to note that Vodacom has made my teenager the target for harassment and they do not want to take responsibility and resolve this issue amicably.