IKEA Refused Warranty for My Hövag Mattress That Started Sagging in 4 Months

I purchased a Hövag mattress from the IKEA Ümraniye store, which was sold with a 10-year warranty. For the past four months, I have been experiencing constant sagging in the mattress. This issue is noticeable every time I use it and has been seriously affecting my comfort. We chose this mattress based on the recommendation of the store staff, but at the time of purchase, we were not informed that it should not be used with a bed base or what type of support it required. We only learned this later from a warranty expert after the problem appeared. I contacted IKEA customer service, but they stated that the mattress was not covered under warranty because of the bed base and offered no assistance. However, since the product was sold with a 10-year warranty, I expect a proper solution to such issues. Regarding my order number 91050851, I am requesting a replacement mattress and a resolution to this problem.