how to restore back my purchase ringtone from itunes store

At the present time, redownloading purchased ringtones is not supported if that's what you're trying to do. You can check your purchase history as outlined here: http://support.apple.com/kb/HT2727, but you can't redownload a purchased ringtone.

I called Apple Care and they told me the only way to restore is buying them back again. Ridiculous, specialy if you are buying a new iPhone and you have to shell money again for your ringtones. They are not back up in iCloud or local backup.