I also had a bit of an issue with the Collector not moving straight away after you give him the 8 Gold Revolvers.
I walked away from the Collector & then approached him again.....I tried standing in different spots....eventually the Collector moved so I could access the key.
If it's still not working try completely shutting down your game & re-starting it.
Try clearing your cache, cookies, history, etc (if you can do that).
How long ago did you contact Pixel support?