Same here -- except I KNOW I've seen it show that it was going to be available in March on my "manage add-ons" screen on EA, which makes this even more frustrating.
It changed about 2 days ago; I was downloading another kit, and when I went to the "manage add-ons" tab, I noticed the download date for my Growing Together preorder had inexplicably changed to April 28th at 1PM.
I am NOT thrilled, and NOT happy that I haven't seen any response to this from the Sims team or EA or anyone, despite seeing others on Twitter mention the same issue -__-
Only thing I can think of on my end is that my game has been buggy AF despite playing it with no CC and only MCCC installed, so I removed the mods from my folder and ran "repair" from the EA app... I can't think of why *exactly* that would have caused the date change/"new" flag, but it's literally the only thing I *can* think of on my end that could have done anything. I mean, I keep hoping it's just a temporary "oops" and won't actually affect my/our ability to download and play on March 16, but unfortunately I also realize it's totally possible that it's something more serious >_<
[Screenshot attached showing April date... I can't remember if it always said "new" after it, though? I preordered I think the first day it was possible, so that seems off...]