Make sure that your boot is not too small or too big. I had the same issuse with my boots/bindings. I had to move my binding like 10 cm. there is a very small threshold of ajustability in griffons. Mabye a few cm at best. If you put your boot in the binding and there is a large amount of silver half cork screwing looking playe then you will need to re-mount the heel peice.
Also if you are moving the screw and it moves then if stops adjusting, you have reached the end of the travel and must re-mount. This is a pain in the ass but is very easy to do. But unless you have experience mounting bindings, nust bring them to a shop. (No ofdence but it would apear that you would not. Considering you did not know if your bindings adjusted. Which is fine.)
I really hope this helped. If it did not message me with questions