Fallhunter, contacting them is the right thing to do. Be polite and contrite. Admit to your failure and ask for an exemption. Sincerity coupled with humility will get you more than belligerence an laying blame.
You are not the only one to miss a rebate. I bought a Remington 380 three days after a deadline for a $50 rebate. I had decided on the gun based upon numerous glowing reviews. I had looked up the specs at the Remington website, but I never explored the rest of the website which housed a prominent rebate offer that would have saved me $50. I bought my gun three days too late.
Marines live by a simple code that if you screw it up you have to fix it up and if that can't be done you suck it up. (Side note: Imised to love the expressions on young Marine Officer candidates when I laid that on them as my career came to an end.)
So I did not appeal for an exemption, I screwed it up and was outside a deadline so I could not fix it up, so I sucked it up, along with a scotch on the rocks. (My error)
If I had simply not mailed it on time I would have appealed and said look, Imbought the gun before the deadline. I would admit I messed up on mailing, but point out that I did buy it in time and I hoped they would not deny me based upon a mailing deadline because being human I can and do make mistakes.
Maybe I would have gotten the rebate or maybe not. Either way it justified another scotch on the rocks. Ok I am going to get a glass with ice in it. Stuff like this should be the worst problem in our humble lives.
One last Scotch on the night table is that if I have to use my 380 tonight to protect against a home invader I assure you the lostb $50 will be forever meaningless and forgotten. It is all about perspective on life. Dont't sweat the little stuff and almost everything is little stuff.