You should never stop taking Xanax cold turkey as it can be dangerous. I'd recommend you slowly wean off it. In the meantime try Valerian Root to help with the withdrawal symptoms, it affects the same brain cemical as Xanax but isn't addictive. You should be able to get it in a chemist or health food shop.
If you are suffering from xanax withdrawal syndrome then please get immediate medical attention as it could get serious.