How to stop h4-h5-h6 attacks?

Title is self explanatory. I do this, and at this elo level it works a lot. But I don’t know how to deal with it when it happens to me, and I spontaneously combust.

Usually when h4 happens, (also includes a4, and h5 and a5 if they’re playing with black) I mirror their move by also pushing my h/a pawn, but they just continue with c3 or something.

Quick Example from a game I just played:

If possible, can someone explain 

1. What would have been optimal in this scenario

2. How to stop flank pawn attacks in general?

It all depends on the position.
The most appropriate is usually a counter strike in the center.
You can also block: h4 h5
You can also counterattack on the other wing
You can also bring defensive pieces like Nf8 to cover h7