Wound Allocation Timing

Kinda a basic question but if I were to assault a unit of Necron warriors with a unit of Wyches, then how exactly would I resolve my close combat attacks?

I might be carrying this over from other editions but I thought if I want my whole unit to target only the Warrior unit then I’d role for all of my models simultaneously and then my opponent would make his saves and that would be that.

However what happened in a game I recently played was that my agoniser hekatrix swung, my opponent then made his saves and removed the models closest to my other Wyches and because they were outside of one inch, they couldn’t attack (not in combat).

Which order of operations is correct?

Wow how many did she kill? Jokes aside,

Technically, its an entire squad going at once, so I believe that your opponent is supposed to wait until you finish all your attacks

Battle Primer, Pg 8, Section 5.3:

"In either case, declare how you will split the unit’s close combat
attacks before any dice are rolled, and resolve all attacks
against one target before moving on to the next."

Your Hekatrix is part of your wych squad, all the wych squad attacks occur at the same time. You should've determined, after your pile-in, how many wyches would be attacking and how many attacks that equates out to. The only way that it would've happen how you described it, is if your Hekatrix was actually your Succubus, thus being a different squad than your Wyches.

Sorry mate, seems like you've been Bamboozled.