ringtones

If you have a copy of them on your computer or on a backup - ringtones are currently a one-time only download. If you don't have a copy of them anywhere then you can try contacting iTunes support and see if they will grant you a re-download, (but they are under no obligation to do so) : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page

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.

You should copy your downloads from your device to your computer's iTunes via File > Devices > Transfer Purchases so that you have your own copy of them

Sorry, but they dont get backed up to your computer when you do a full back up or to iCloud. This is not a problem of not backing up, but a problem with Apple. This is exacly what I was told too by the Apple care representative.

"Sorry, but they dont get backed up to your computer when you do a full back up"

Correct. That is why he told you to transfer them as you should do any purchases.

All you have to do is transfer them to your computer.