Check the comreg website, find out who the short code is registered to, send lots of letters, threaten them with comreg if they don't sort it out.
Just in case anyone else is reading this thread with similar issues - where the subscriber (to the ringtone/other service) is a minor, be sure and let the service provider know they cannot enter into a contract with a minor and demand a refund.
I have successfully done this twice (you'd think my daughter would learn!) and got €50 in one case and €70 in another - sent in cash strangely enough!