United Propane Gas Mammoth PropanePaducah, Kentucky Did not receive all the propane I paid for but getting bills for $254.33 Glasgow Kentucky

We paid in advance for 500 gallons of propane last year before the cold season. The company did not fill my tank when gas was requested and still owes me another 100 gallons of propane. This company (United Propane Gas) is billing me for $254.33 after the season with no explaination as to what it is for. When my wife talked to a woman at Mammoth Propane here in Glasgow where the gas was paid for, she claimed they had to pay more for the gas and that my wife had signed a contract that would allow them to charge more forgas but evidence was not presented to want they paid for gas. Also if they can charge more, why demand advance payment to lock the price in? Woman with Mammoth propane told my wife we still had 300 gallons at the prepaid price we could get later. I'm sorry but I have trouble believing her.  No mention was ever made of gas price when my wife called for their little 200 gallon delivery.  Is it not illegal to take advance payment and not make good on the promise? I had trouble with this company in the past with water in the gas. They were telling me my tank was sweating inside when it contained gas under pressure and wanted to charge me for putting alcohol in the tank. I have dealt with a couple other propane companys with no problem other than paying a little more for the product. I am angry with my wife for dealing with this company again. I would advise anyone dealing with this company to be very careful.