Disappointed: Mock-Up deceiving to actual print

I have been ordering from Sticker Mule for quite some time and this is literally my first bad product review. When I approved the preview it was because I could still see all of my letters on the rainbow background which is the mock-up I requested to send back for changes, asking to see it on the silver glitter background the stickers were actually being printed on. I asked for that so I could see if I needed to change the colors of my letters. The response I received when I asked was: (The glitter rainbow effect is part of the proof only to help illustrate the material and will not print. You can see examples of our glitter material on the product page.) When you guys printed the first sticker, at what point didn't someone think to say, "Hey this doesn't look good. You can't see all of the letters."? Now I have 50 stickers I can't do anything with. I would order again as long as I can see a true mock-up of what I actually will be getting. From these 50 unusable paid for stickers I can now see that I need to change my colors. I believe it would be better if clients can see the full picture to save on time and money.