Arrears on a new contract within days

This shocking I opened a contract with this company on the 3rd of May 2023 but today I'm in arrears with 400 and odd Rands. How is that even possible? And to top it I cannot use my own router to connect but I'm in arrears. I have not used that data to data. What the hell? I want them to cancel this contract I cannot work with the likes of this company. So disappointing