Vodacom leaves me to be harassed and threatened

I have been phoning Vodacom repeatedly to have my number changed on my contract as I have been receiving phone calls from someone who is threatening me and making demands for money. Vodacom Keep telling me that my account is in arrears and that I must call them back. This has been going on for 3 days already. My nerves are now at their end and I cannot believe that Vodacom can be so heartless. I have been with Vodacom since I had my first cell phone and I’m now beginning to doubt them and their extremely poor level of customer service.