Vodacom can't be trusted

I had a contract with Vodacom which ended in September. I paid on time every month. This month they send me a quotation through email with my number upgraded to a sim only contract without my knowledge. When I call to ask them to cancel it, they said I should wait until month-end to cancel a contract I never took. How can I pay around R570 for sim only whereas I failed to upgrade to a R400 device?

Worst customer service