@Candycreeper
I can't make up my mind about this one.
On the one hand, I find it annoying when people don't remember my birthdate/get the date wrong. I mean, people who have known me for YEARS, family members, and other people who I buy cards and gifts for. (And I never get THEIR birthdates wrong!)
On the other hand I don't know why you are so bothered, (and clearly offended,) as he is an ex anyway. I would just email back and say 'why are you wishing me happy birthday? My birthday was nearly 2 weeks ago?!' Wait for his response and then block him.
If he doesn't even SEE your 4 kids you have with him, then you don't need ANY communication! Block his email address, block him on your phone, and block him on facebook/twitter. (If you have him on there.)
Did he remember your birthday when you were together? Did he have 'form' for forgetting dates?
Me and DH have been married 20 years, and our anniversary is the 17th of July. He still asks me at the beginning of EVERY JULY 'what date is our anniversary again? The 19th?????' (Or the 16th, or the 13th?!) He is not being ignorant or rude, he is just a man. Men are not the best when it comes to this kind of stuff. (IMO, and IME.)
How odd though that he is wishing you happy birthday when he can't even be arsed with his own kids! I would be tempted to email back to him, and say 'my birthday was 10 days ago, not today, you fucking arsehat. Now piss off and don't message me again!' Then BLOCK him!