So i had my waterpump replaced and later on that night the harmonic balancer pulley bolt backed completely out 

now i ordered new belts and the bolt with the locking key and it happened again 2 weeks later !!!

Anyone have this issue or can point me in the right direction ?

How did you torque the bolt up in the first place? However you did it must not be adequate and the vibrations are causing the bolt to back out

I have torqued a Crank pulley on a VG30 hundreds of times and never once had the bolt back out

Torque it properly and use some red loctite just to be safe.

I use the most recent milwaukee 1/2 high torque impact with one-key that allows you to set the desired torque via an app (most useful for lug nuts) since the impact is super strong & is capable of shearing the bolt head off anything.