Incorrect pricing on goods on special

There was a special on sheets in December and I needed to get two. The shelves were a mess and finding the correct sheets was an issue. When I eventually went to pay for them I was charged more than it was supposed to be and the cashier advised that there was no special on sheets. (One fitted or flat sheet with two pillow slips). I was annoyed and then even more so when I got home and realised that one of the sheets was a flat sheet instead of a fitted sheet. Unfortunately I had already taken it out of the wrapping and thrown the wrapping away. When I complained I was sent a voucher for online orders. I don't do online orders and after that experience I don't think I will easily go back to Mr Price Home again.