If you don't realize you have to jump through this dumb hoop and think you are actually getting the discount automatically, which is quite easy to do (I did, and I'm no dummy), they do not reimburse you the difference if you call on the phone to explain. The guy on the phone specifically explained to me that that is their official policy in this situation.
I mean, I trusted Lenovo (good past experiences), so I wasn't being super duper careful to look for any kind of trick. Imagine that... not looking out for being tricked! What a fool I was.
If you eally want the discount, you have to cancel your order and re-order, which means getting the product later. Lenovo knows very well that many customers won't do this.
tl;dr Lenovo suits have calculated a new way to trick customers, and treat customers in a shitty way. They should be ashamed. Gipped me off for a few hundred bucks.