Rotech Healthcare – Do not order accessories on-line

I ordered a chinstrap, size Standard, since I have an average size head. It arrived in a sealed bag. I had to cut open the bag to check out the size. It seemed well made, but was much too small, so I never put it on. When I called, I was told that I could not return it because I had opened the bag. How am I supposed to check the size, if I cannot open the bag? Now I am out $17.50.