Poor guaranty for sleeping bed

I bought a bed in 2019 around february it was 4000 early 2020 i return it back because it was given me a problem their mattress is not strong then they give me back my money i purchased ather one same store that one was 5000 same thing the problem is the mattress bought atound March then i went to store to complain about the bed was told my bed doesn't gave guaranty because they are counting the 2019 purchase how come the do that to different bed different amount they know their bed are not the best i goner fight this it not fair please help