BAD SERVICE AND RIDICULOUS BILLING

I app**** for their internet last month February 2023, the router arrived on time and i paid an installation fee or pro-rata data since it was in the middle of the month, My agreement with them was that I will pay R199 per month for 24 months contract. Today i was charged R555.11 out of the blue and i fail to understand why because even my statement sates that i pay a monthly instalment of R199 per month