Over charging and not being able to assist

I have a contract that is supposed to be billed at 499 and you now charge me 848 and that is un exceptional. First i signed a 24 month contract and you now made me a month to month. You also made my data 5gig instead of the 1gig i signed for. I have upgraded and i am also bei g charged for my previous contract even though the 24months have passed. I have been to a store more than 5 times called you more than 5 times. Please fix your problems and stop waisting my time and money you are giving the worst service i have ever received and if you dont fix you problem and credit me i will stop my contract and move to a provider that wont take my money and not give a service.