Princess Cruise Lines – On board shopping

I purchased a pair of earrings on board. The receipt claimed I purchased two identical pairs and charged me double. I had no idea until received my account summary after the cruise was finished. I have pursued this through every channel given to me and still I’m told there was no error and I have to suck up the double charge. Instead of $40.80 I was charged $81.60. Why would I continue to chase $40.80 after spending thousands to sail (premier package guest) if I didn’t know I am right and the sales assistant made an error?