wrong furniture

I bought a bed for my mum in October 2013 and the bed was delivered to my mum I did see the bed upon delivery to see if it was the correct bed. Last year the stitch on the side of the bedstartd coming loose, my mum went to Lewis to tell dem abwt the bed nd when they checkd on their system they asked for the bed name and they realised that they actually gave us the wrong bed nd da bed I hav is a bed for r3000 nd am payng for a bed worth r4000 they then told my mother they will come fetch the incorrectly bed, when my mother went back to ask when are they comin to fetch the bed they said they will never fetch it as my account is in areas and that I will continue paying the amount of a r4000 bed wen we have a bed worth r3000. Plz help