Mattress Warehouse, Centurion, bad service

We initially bought a mattress from Mattress Warehouse in Centurion. We returned the mattress within the 100-day prescribed period. The mattress that we then decided upon and paid for was more expensive than the first one and we paid the shortfall. However, before the mattress could be delivered, we cancelled that purchase and finally took another mattress that suited us better and which was cheaper than the second one. The reason for these exchanges were due to the fact that a reasonable comfortable mattress is expensive and has to last for quite a few years. We worked out that, because the final mattress was cheaper than the second one, there was a substantial amount owed to us. The salesman was asked to check the figures that we worked on against the figures that he worked on. The salesman promised to investigate the matter. That was in the middle of October 2018. We never heard from him again. We have followed up numerous times but just cannot get hold of him. The impression that we get is that he is ignoring us on purpose.