Boardmans Returns Policy!!

I'd like to query Boardmans return policy: Last month I bought 2 sheets on a sale. I was then out of town for 3 weeks. The one sheet was a queen size, but I needed a double size. I thought I'd go back to the same Boardmans store and simply exchange it for a double size, via the Cashier. The packaging was unopened. To cut a long story short, I was told I owed the difference of ~R140, meaning I had to purchase the double sized sheet at full price (as the sale had ended).<br> <br> As I said to the Cashier (as well as what seemed like the Cashier Manager), if I had picked up a double sheet last month (instead of a queen sheet), I would have got a double sheet at the sale price - what difference does it make? All I want to do is exchange the queen for a double (exact same product - same colour, same make etc). So option B was to return the queen sized sheet, which I did.<br> <br> My next move will probably be to return the other sheet I purchased.<br> <br> The result being that Boardmans will have 2 sheets in stock, that were previously sold - surely Boardmans is in business of selling.<br> <br> Must I take my money elsewhere, Boardmans?