I accidentally scaled one of my players... And now he can't get 20 ft. within the radius of a cactus or high-wall... PLZ help. Love you.

In theory you can just rescale the player back to 1.0, but if that doesn't work, you can always have the player die and then disconnect (without respawning), which will destroy their player object, thus resolving the issue. When they reconnect, a new object will be created for them since their previous one is gone.

I changed the player's size and now he can't walk, I already deleted the plugin, the player re-logged 20 times

Did you follow the instructions exactly? When they die, they must not respawn. They must disconnect. Only after they reconnect should they respawn.