Metro PCS - CORPORATE CONTACT INFO. Charged for month my phone was deactivated Dallas, Texas

I have a metro PCS account. I did not pay my phone bill on the 17th of September so my service was suspended. I paid my phone bill on the 9th of October, and thought I was good. I then found out that my phone service was disconnected for not paying my bill on the 17th of October. I called and asked metro pcs about this and was told that my payment I had made on October 9th had been put towards the bill I had not paid in September. I'm sorry but the terms and conditions on Metro pcs website says they are a pay as you go company meaning you pay before you use your phone. I did not pay in september so I did not use my phone in september adn then I paid in october meaning I can use my phone in october. So if they are pay as you go then whay is the bill I paid in October get put towards the bill in september since my phone was never used in september? I asked about this and was told there was nothing they could do and if I wanted to starighten this out I needed to pay 5 dollars to get my billing cycle reset so that instead of my bill being october 17th it would have been november 9th. However they said there was no way they could waive the 5 dollar fee to recycle my bill and basically told me to pay my phone bill again or my account with the company will be cancelled. How is it legal for them to charge me for service I never used when they advertise to be a comapny that only charges for what you use?