shoes(slippers)

On the 26 November 2015 I bought slippers for someone when I fitted the person the slippers they were small so I returned the slippers to get the correct size, they told me they don't have the size that I wanted and I must leave the slippers and come back to check if they have in stock, so now I went to check if they have the correct size which they have now but they can't give me the slippers because the prize is increased so I have to pay the amount, the slippers that I bought then was R365 now is R545 which I have to pay R180 the employee called the owner and the owner said I must pay that amount, I asked the employee to give me the slippers that I bought the small ones she refused she said the owner want me to pay the amount because the prizes are increased PLEASE HELP.