Attention to the fabric COVER bought more

This cover is not adapted to this cushion, error by the manufacturer because the zipper is in the middle of one side and not on the thickness as in the photo (see cover sissel cushion), so you can not not put it on. I asked for the return and refund. To cushion itself, I can not remove from the air even by what is stated in the instructions, not one "puff" of air comes out, unless someone can explain me better how to do it, (because I wanted to remove the air cushion to soften it, thinking that I could put as a fabric and foam cushion) .Please