Vodacom offer for data bundle

I was contacted by Vodacom offering me a 2 GB data contract for R107 per month. They gave me all my Vodacom information - account details, numbers active on my account, etc. They phoned me about 7 times about the offer and eventually I thought it might be a good idea because apparently my son buys a lot of extra data. When I spoke to him last night, he said it doesn't work since you have to swop sim cards. When I wanted to cancel it at ***, the number given in the sms informing me about the vetting application, I discovered that the numberdoes not exist. I would like to cancel it but where?