Aerie/American Eagle review: Unauthorized payment amount on online order

Checking out on aerie website, when the order was placed I had 10 items as part of a 10 for 35 dollars promotion. I authorized 42 dollar total at place order and checkout. Instead they only sent 7 items and charged 89 dollars. They claimed they were out of 3 of what I ordered so it was full price for everything. I authorized 42 dollars, not 89 dollars this has to be illegal. Customer service was very unhelpful and unapologetic, they gave me a 20 percent off coupon and a return label. They are making no attempt to fix this and I know they are doing it to many other people and they are being stolen from. I wish I had the screenshot of checkout but when you submit it takes you to a different page with your order number, I didn't think it was possible or legal for them to do this and change the total.