hotels.com expedia.com they over charged and refuse to give my money back Internet

I boked with hotels.com, thought i was getting the best rate, when i get to the hotel to my amaze i overheard some checking in , they were getting a 52 dollar a night rate while hotels.com charged me 70 dollars a night. i dint make a big deal becuse they garranteed the lowest price. i continued with my vacation as planed at check out time to my surprise i receved the 52 dollar a night on my recipt but no credit was given to my account i called and called spoke and spoke ut no resolve they wanted to give me a 50 dollar voucher for hotels .com but i refused since i paid in cash they made 75 dollars extra off me. that is not right, when they were offering at the hotel 52 as a rate just walking out of the street .....hotels.com is a scam and a  rip off and unaceptable, no one should go through this on their aniversary vacation.