Vivense Refuses to Exchange My Mattress and Ignores My Requests

Vivense sold the product as a special production, but there is nothing special about it. It feels like a trick to prevent customers from returning the product if they do not like it. When the mattress I purchased turned out to be too thin, I wanted to initiate a return to exchange it for a thicker one. Despite repeatedly reaching out to Vivense, I received no response. The lack of communication from such a well-known brand is truly disappointing. They simply say, "We cannot take action." I cannot understand how a product with an unopened package cannot be returned or exchanged. I am requesting either a partial deduction and a refund or at least communication to proceed with an exchange.