discreet company policies

i received a R500 gift voucher to be used at the Body Shop. I went to The Body Shop i and chose an item to the value of R500. Next day i had a change of mind and went back to the shop with the original receipt and item in its original package. I told the sales assistant that i wanted to return the item and would at a later stage spend my voucher when i found something of interest. The sales assistant stared at me blankly for a few minutes then said she i had to take an exchange there and then. I advised her that i did not want anything at that stage and asked for a credit note instead. The sales assistant said nothing and went away .20 minutes later she returned and told me that she had spoken to her manager and it was company policy that no credit notes are passed on gift cards. The following Monday i received a call from the manager who confirmed that nothing could be done- it was company policy and that i was to go back to the store and find something to the value of R500. If a company has a policy of this nature surely its drawn to the consumers attention at the time of purchase and should have the relevant signage in the shop. Appalling attitude and customer treatment !