I feel for you i really do, i suffered with a nut case similar to ths and it went on for over 3 years and Linden did nothing to help even though this freak managed to get all my personal information and a photo of my kids and threatened to post the pic and details on porn sites then come cut all our throats. I was scared out of my mind and all Lindens seem to come out with was Create a New Account. I had alreay made several new accounts but the nut case alway found me via friends. Lindens didnt help at all and didnt seem to think it was serious even though myself and several others filled complaint after complaint.
I took things into my own hands eventually and contacted the police who then dealt with the situation. Lindens Lab could surely ban the isp of these people that seem to go out of their way to cause hurt and upset to others. A few days ban to an individual that is doing physcho things like this isnt harsh enough and they just ceate alts anyway. The guy I had issues with had approx 20 alts and probably more I didnt know about.
I wish u all the luck in the world and hope that you can resolve this problem quickly.