[MD Longhorn]

There are three things you did not say that are in play here.

First - you say the ball is in the plane of the net, and I assume you mean the horizontal plane of the top of the net. The important unanswered question here is whether the ball has crossed the VERTICAL plane of the net.

If it has not - the actions by the blocker are illegal. You cannot block a setter setting the ball if the ball is entirely on the setter's side of the net.

If it HAS, this play by the blocker / hitter is actually coached at the highest levels, and is legal.

Second - if the ball has touched the vertical plane of the net, thus making the defender's block/hit legal - you did not say whether part of the setter's body (usually hands) was above the horizontal plane of the net. If not - if it's just the ball crossing that horizontal plane, the actions of the setter are legal and this should have been a no call.

If the setter's hands were across the horizontal plane of the net while contacting the ball when (or after) the defender contacted the ball... then the setter has, indeed, blocked the ball.

Third - you do not say, although you imply, that the setter is a back row player. I'm assuming she is - and if she is, the block by the setter is, in fact, illegal and your referee called it correctly. If she is not, of course, this is nothing.

So it's possible this referee's call was correct. If the ball had crossed the vertical plane of the net, and the setter was indeed a back row player, and the setter's hands crossed the horizontal plane of the net when she contacted the ball... the referee was correct. If any of these are not true - your referee erred.