Poor quality mattress

I bought a bed and headboard in March/April at Fair Price Festival Mall. The quality of the mattress is very bad the sides is not even.

I went back to the store to request an exchange. They sent a driver to collect, the driver came and collected the mattress then after a few hours, the driver returned with the same mattress claiming that the warehouse manager rejected it because it's torn underneath. The mattress was very clean when they collected it now it's dirty.