Being over charged

I have been with T-Mobile since 2012 and am now irate!  The problem began in April 2021. I paid a $400 + bill in full.  Two days later, receive a notification that my new bill was $400+. So, I immediately contact them as the bill that I just paid was the amount that they stated I owed.  After speaking with several CSR's  ( all of whom attempted to tell me where this trailing bill came from) I asked to speak with a supervisor.  We audit the bill together and then end result was that I would receive a credit in the amount of $160.00.  Move to the present. Made a payment arrangement for Sept bill. I was told that my bills generate on the 20th of every month.  Paid $414.00 Oct 12th then immediately get text message of past due for $347. Paid that and immediately receive another notification that $347. again is past due????  If you pay the amount due in full, then where is the extra bill coming from? Well, move forward to Nov 18 2022, I decide to do my own audit as there has to be a trailing bill somewhere. Receive call from nasty CSR that states if I don't make payment arrangement they will shut it off. My response, " shut it off." Because there is no way that I am paying $1100 for phone service.  That they need to audit on there side as they are charging too much.  Complete my audit and it shows me that T-mobile never gave credit and that they charging me $ 347.82 that I simply don't owe them.  Call and ask to speak with a supervisor and the CSR spent 30 minutes on the phone trying to explain away their descrepency.  Then she tells me that my new bill generates on the 24th of each month.  Which date is it? The 20th or the 24th??? Instead of investigating and doing something about this extra bill, nothing except they want me to make payment arrangements which I hate because they charge additional fees. T-Mobile states that they do not pro-rate bills. Look at your bill.  Because it is pro-rated and they are charging a month in advance.  So disappointing.  After a decade with them, I will be finding another company! Unfriggin believable!