“Botox not injected properly? it seems to be a guessing game”

Seeking help:

The first time I got Botox it worked beautifully but wore off before 6wks! I believe it was watered down...the 2nd & now 3rd time I paid significantly more but it is not working between the brows. The docs get very defensive when I return- I don't believe they are putting it into the proper muscles in that area as it has worked nicely in the middle of the forehead (which I didnt even ask for..) How do I approach this? Should they inject a bit further out above the eyebrow perhaps?