First time user

I had downloaded the app on Saturday and made a purchase using my 30per discount. on checkout they charged me the full amount. today when I call them to remedy their mistake,they ask that I pay in full for my first purchase and there they will make up a new discount for me on my nxt purchase. when I tell them that I chose these items only because of discount they say they cannot help. I will not pay for my order and allow it to lapse. luckily I opted for an eft. I will never use them again and will delete their app. terrible service for a first time customer.