Vodacom gave my number to someone else

I app**** for a contract phone and the lady asked me if I want to keep my old number and I rep**** yes because I had my number for many years and I do business from my phone. When I spoke to vodacom again they said I cant keep my old number because it is already on a contract. I said it is impossible because my number has been on prepaid all the years. So initially I thought ok maybe I am approved and there is just a mistake. Then I received a message do you want to do a sim swop and I rep**** no because it was strange to receive a message like that. Then on saturday morning I was still on whatsapp when I'm on wifi but when wifi is off then my phone say emergency calls only. I thought something was wrong with the network. When I met my client she mentioned if she phones me then a guy answers my phone. He said to her his been receiving many call from people looking for me. I phoned vodacom from a friends phone and they said no my number is on contract and belongs to someone else now. I said how is that possible? The lady said you deactivated your number. I said to her it is impossible why whould I do that, then she rep**** you didnt you your phone for more that 3 months so that's why it's deactivated. I'm furious, I am a real estate agent and also owns a hairsalon, why would I not use my phone for more that 3 months. She said they will investigate and get back to me in 7 days and she needs an alternative number. I gave my husbands number so she can send me the refererence number which she failed to do. When I message vodacom they keep asking me for an alternative number which I dont have. I'm still using my whatsapp on my old number and the guy who owns my number agreed not to register for whatsapp so I can still use my phone and old number in a way when I'm on wifi. He also went to vodacom and asked them to give him a new number so I can have my old number back and because he receive to many calls from people looking for me. I went to vodacom yesterday and all they say is well we can not give your old number back because it is on contract now. I am very upset and I want my old number back, they messed up and I need answers. I am busy to loose clients and business and I refuse to take out my sim card and put a temporary one in because I will loose all my whatsapp. This needs to be fixed, their responsibility, their mistake. I've tried everything. What is the next step?