SAGGING MATTRESS

Bought the 137cm hotel plush mattress on the 03/04/2021 at Sleep Zone N1 City and started seeing that the whole mattress is sagging on the one side after only 2 years. Was told that we would receive a 12 year warranty. When we made contact with Sleep Zone, they advised that the warranty falls away if any stains are on it. There were no coffee stains only abit of sweat stains from sleeping over the years. This is very unfair as this cuts no ice. selling a mattress that only lasts 2 years ??? EXTREMELY DISSAPOINTED SLEEP ZONE!!