Refund not received in full!

I bought 4 items 2 pairs of sunglasses, a tank top and a vest, The vest was on sale and the other 3 were full price. Of the 3 items that were full price I was able to use the R100 discount voucher (Spree terms and conditions clearly say you can't use a discount voucher on something that is on sale). So I made sure I reached the minimum required R250 to use the voucher on full price items. Then I added on the vest which was on sale. When I received everything the tank top and the vest did not fit so I sent those back. I got an email from spree saying I would get R211 refund. The refund came at R157.04. When I sent an email asking why the refund amount was less, all I got back was an email saying we refund what you pay. I paid more than R157.04! When I called the call centre they said Spree deducted the voucher amount on the sale item. How is that possible when spree's own terms and conditions say you cant use a discount on a sale item. If I hadn't bought that sale item (which wasn't necessary to apply the voucher), I would have received the full amount of that vest. Even though the amount of money in dispute is low, this doesn't make sense, Spree can't set rules to suit itself!