Scooter problems can someone help?

im not sure wht these parts are technically called but im gonna do my best explaining what's wrong.the problem is the gear belt that goes to the rear tire broke, and the end gears to which the belt is connected are extremely hard to get of. there are nuts at the and of the gears but are so tight that we couldn't pull it off with two people pulling(while using as much torque as we could). even if we could muster u enough strength to take these nuts off, the gears spin with the bolt! so anytime we make an attempt to turn the nut off we have to jam the gear with a screwdriver, which inevitably slip off. we cant seem too pull it off, even though it sounds so simple you wouldn't believe how tight that nut is...so now i ask for opinions and help on how we can pull this off.