Arrogant behaviour towards customers

I did a laybye with the store for couches and I was provided with a contract , I paid R6000 towards the laybye after the level 4/3 restrictions when they were allowed to trade I went back to the store and requested that they change the couches to a bed set which was R4200 and with the balance of the money R1800 put in a new laybye for a Chester drawer , this was done and proof of such was given to me.

I recently went to collect the item bedset and requested they cancel the Chester drawer but I was then told that I cannot get the bed for R4200 anymore and that now I will get it for R5400 even though they had already given me an invoice for R4200. I disputed this with them and they then said that I was suppose to be given a new contract when I did the change but I responded to them in saying that was their responsibility and not mine.They treated me with the most arrogant attitude and they told me that there is nothing I can do about it. I then said to them they should rather refund me my full balance that I had already paid R6000 but I was told that it won't happen they will charge me storage fees and there is nothing I can do about it.