On Wiktionary, we have a user who's been permanently blocked many times, but seems to have an infinite IP range, so he (or she) simply creates a new account and continues editing. What can be done? PS I apologize if this is not the right forum for this message. Feel free to move it if necessary.
Topic on Project:Support desk/Flow
As you now have the ill-fortune to discover, it's rather difficult to prevent a dedicated user from editing (see Wikipedia:Long-term abuse). The options at your disposal are likely to be either ineffective or undesirable. They include complaining to his ISP, blocking his ISP, and writing an edit filter.
Your CheckUsers should be able to tell you more.