IR or nothing?

[Scrapper1]

As always, NCAA-W rules.

This situation came up today while I was R2. Visiting team serves and home team loses the rally. So there is a rotation. There was some confusion on the home bench about whether someone was going into the game. The R1 waited a few seconds, then beckoned the serve. Right after the whistle for service, home coach yells, "Yes, sub" and a player steps into the substitution area.

1) At this point, do I have to blow the whistle (since the player came into the substitution area)?

2) Regardless of the answer to #1, I did blow the whistle. So this becomes an improper request, correct? Penalize with a yellow card, warning? And no sub is allowed?

To make it really strange, the "sub" was actually replacing the libero, who had just rotated to the front row. So when I denied the "substitution", they automatically had a position fault.

Did I totally screw the home team? Did they do it to themselves? Or some combo?

Now that I'm thinking about it, could they have taken a time-out and then replaced the libero?