Billing quiry

I joined rain in December during their black Friday special. I was told that i was going to pay a certain amount for pro-rata. I did pay for it after too many questions. A week later I was the requested to pay another amount. All in all I ended up paying R499. 00 in the month of December. I then got a message after the 1st of January 2025 that I owe them R1655. 00.ive been trying to get hold of them with no luck. How did it get to that amount when I don't even have a full month using it? Rain is just a **** guys trust me. Stay away from that company.