over billed their customers

so apparently since May 2024 your total bill with T mobile only allows you to pay the past due now I was told not the total billed! So my bill was 546. in May 2024 I paid that but when you make a payment arrangement to pay the 546 you are only paying 300 of that so that will carry over fees and then they say to avoid interfering you will pay additional 20 dollars a line, but what you are not knowing they have already charge the previous month and the interruption fees are there rather it’s turn off or not! How can you pay unlimited data and service for 50 a month and it doubles when you pay your phones off! I have been paying double since 2023 and this is not right. So I came from 336 a month faithful to now 900 a month with no updates or upgrades! I own my phones and who will pay any phone service  300 a line that is what they are charging