Connect your phone to iTunes and under Ringtones (select your phone on the left column and then click on ringtones in the top center of the main window showing your iPhone Summary), UNCHECK the box and sync.
Once the sync is finished, close iTunes and reboot your phone (You do not have to disconnect from the cable if you don't want to)
When the phone comes back up, launch iTunes again and this time go to ringtones in the left column and play one of the ones you either created or purchased to confirm it's working in iTunes.
Then go back and reselect the box you unchecked either and sync again.
After this sync finishes, disconnect the cable and test your ringtones on the phone.
Make sure that the silent switch is not down, and that the volume in the settings for Sounds is all the way up, and then select your ringtone.
Once the ringtone is selected (and you were able to preview it), reboot and test again with an actual call to your phone.
If any of the steps I posted above fail, then I can only think of one thing that could cause this. You are not signed into the correct iTunes account. (whether that's true or not remains to be seen, but that's the best I can think of)