MTN Cell phone company is ripping of consumers

I entered into a new cell phone contract with MTN on the 24th of December 2025. A week or 2 later I get an sms that my tariff willl increase, although no one mentioned that they are having an increase the next month. They vill by first month at end of January and a whooping R11600. In February. No ine can tell me how they arrived at that amount.