he means to remove the ankle strap and replace it in a lower set of holes down the heelcup - so that the strap hugs more over your instep and less up on top of your ankle.
i kinda doubt that that's gonna do it, but i do think that your bindings and the way they are set is what is causing your problem.
what is your forward lean set at?
have you tried moving your stance closer together some more yet?
from everything you have said it definitely sounds like you need to square yourself over the board and keep more weight on your front leg. you may also be standing too tall.
if you can throw a vid of you riding up it might help.