Mattress good, bad zipper

The mattress I am very pleased to be have being selected with a body weight of 55 kg H3, as I have already had the experience that I H2 is too soft.
With the zipper I'm not zurfrieden. The zipper can be, unfortunately, with the best will not open, it seems to be somehow stuck. The seller has not really responded and I have no desire to send the mattress back. A bit annoying it is anyway. Will probably, if I really want to wash it out the terms resort to scissors and sew up the place again afterwards. Hope it works out.