Labor day coupon experience

I went to your store in Commack NY with my son. We went there to pick out some books for his 11 year old team mate who broke his hip this last Friday. We were excited that another team mate shared a coupon that they had received via email for $10 off a $20 purchase. We took quite a bit of time to carefully pick out just the right books. We got to the register and as the cashier was ringing us up Lindsay another cashier came over and advised our cashier that our coupon was counterfeit. Needless to say I was surprised at this news--I know several people who received and used this coupon with no problems. I then informed the cashier that I did not want the items, and crumpled up the coupon and put it on the counter. At that point I said nothing else. Lindsay continued to berate me in front of a store full of customers while she happened to be waiting on my neighbor. I can not tell you how mortified I was. I reiterated that all I said was that I didn't want my books and was leaving, she kept going on about my attitude. I'm very sorry but Lindsay has a very poor attitude and very poor customer service skills.

I feel Borders owes me an apology. I would also like to know if the $10 off $20 coupon I received was valid or not. If it was I feel that Borders should compensate me and my son so that we may go back and purchase those books for his team mate. (we were each going to use a coupon)