Taking money and ruining credit

Sprint i thought was the best service out there besides Verizon I was not having any problems and then one day i was late one day late on my payment and i payed it over the phone and they took double the amount of money out and tried to tell me that I owed that after being not even a day late. I authorized them to take one payment out and they took two when i didnt even use the service the next month because they shut off my phone. And still told me that i owed them the next months payment in advance! No one around me will ever buy another cell phone from sprint not as long as the people they have doing billing are still there.