Bounce Energy Charged Large Cancellation Fee one week Before my Contract was up Nationwide

I mistakenly cancelled my electric service with Bouce Energy one week before my service contract was up. They charged me a $240 cancelleation fee (the entire amount) and would not prorate my charge even tho I  had only one week left on my contract. I was recently told by someone with good knowlege of the electric services that I should not even have had to pay the cancellation fee unless my provider itself was changed. It wasn't. I have contacted them about this and asked for my money back but they have not responded. I think they cheated me and are cheating a lot more people too.