Vodacom, I am Tired!

I am struggling with Vodacom's billing. I took a R399 PM home data contract with them in November 2021, I started paying in December and it wasn't the amount we agreed on, every month im paying more than I should. When I contact them they tell me its "purchased content" and they block it. but the next month I've to go through the same thing. its only been 4 months into a 24month contract and already Im tired! This sim card is in a router, no one fiddles with it, how is this "content" purchased. What can I do for Vodacom to charge a fixed amount as agreed on our contract.