Are both okay here: I would have contacted you if you hadn't called me first. VS I

[B45]

Are both okay here:

I would have contacted you if you hadn't called me first.

VS

I would have contacted you if you didn't call me first.

 

[Rover_KE]

Only #1 is OK.

 

[MikeNewYork]

For me they both work. The word "first" establishes the order of the past acts. That makes the past perfect optional in my opinion.