Mattress World wont give me refund or help me with delivery fee Roanoke, Texas

I just recently purchased a mattress set from mattress world on roanoke, tx. I have bad credit so their no credit check was really appealing to me considering I had to get a mattress due to my lower back issues that consist of 3 herniated discs and nerve damage. I told the sales person what was going on and what my doctor told me I needed and she then proceeded to show me every single mattress in the store because she really didn't know a whole lot about them. I finally found the one and only firm mattress they carry and decided to give it a try. I informed the sales person that there might be chance that I would have to exchange the mattress if I sleep on it and don't like it. She just said that's not a problem and she would exchange it if necessary. There was no talk of additional delivery fees at the time so I pretty much had to assume that there wouldn't be one. Well sure enough I got the mattress, slept on it last night and it was bad. I contacted the sales person and she said that there would have to be an additional $50 delivery fee to get the exchange. I was immediately alarmed and made her talk to the boss man to see what he could do. He didn't even attempt to help me and told me 2 different times that he would not waive the fee. I informed them that I am paying hospital bills on top of my other bills and I just can't afford the additional $50 fee. I wonder if it would've killed them to waive that fee. It's just an exchange. Do we have to pay to exchange things at Walmart? Also, when I told them I just wanted to return the mattress they refused to take it back because I supposedly contaminated it. I slept on it for 7 hours after I took a shower. I really don't see how that falls under the contamination category. So now I have to use bill money to pay the delivery charge. I hope I have electricity next week. Thanks mattress world, you really bent me over this time. Companies like that need to understand that not everybody is made of money and that some people need a little help. They need to be more informative in their policies and products as well. I hope this helps anybody looking for a new mattress set.