Keeping the same number from prepaid to contract

I signed Up for a SIM only contract with Vodacom online.Yesterday the SIM card arrived but I wanted to keep my original number (a Vodacom prepaid number) on this new contract. I’ve tried reaching out to customer service but it seems there’s nobody that can help. The Vodacom support Twitter account doesn’t reply, the chatbot TOBI doesn’t help and when you speak to a Vodacom agent, they say it’s not possible and that you’re supposed to choose the option to keep your number when you order it online - however there was no such option. So now I have to keep a useless contract or I have to pay for them to cancel it.