complaint for genius bar

I am sorry to hear that you had a bad experience at a Genius Bar

1. Contact the Manager of the store you have visited
2. If you have already done so, and the response was unsatisfactory and/or you are unable to get back to the store, you can contact Apple Support to talk to an advisor regarding your experience at http://www.apple.com/contact

Apple United Kingdom:

0800 107 6285

A "formal" complaint is best when you send a letter via postal mail to the company rather than a phone call. Send it to the store manager with a copy to Apple.