Sagging matrasses

We brought a cloudnine matrass a few years back and was so happy and still is with that spesific one but then 2 years back we brought a cloudnine for our son but then it started sagging right down the middle from top to bottom and i reported it to the strandfoam gauteng where the send out an inspector technician his name is Calvin Stephenson he came out and said yes he can see that it sagging and that it is a problem cause it is not human sagging. So eventually i got the report that said there was no problem found and that there is not any manufacture problem which i totally do not agree because the matrasses says 8 year guarantee and after emailing calvin back and said but this is not what he said they and all of the staff just never get back to you even the manager JC (dont have surname)