Poor Repair Excuses.

I logged a call for a repair on a mattress that I am still renting from Teljoy. The foam is starting to break on the top. I have just been told that the supplier will not manage the replace or repair as the mattress is dirty and the voids the warranty. FIRSTLY Surely there is something know as wear and tear for a mattress that is 2.5 years old. and for something that you have to flip over constantly which also for this mattress is a TERRIBLE design as there is no foam on the other side and a GAP in the middle. How is that supposed to be reasonable. SECONDLY that has NOTHING to do with the issue at hand. This seems like a poor excuse from the supplier and I need this taken further with someone from a management level asap.