This juvenile behavior just degrades the profession. If a client isn't paying you, take it to court. Or, if there was no contract, as in this case (OP states so in the comments), then learn from your mistake and move on.
Legal issues aside, I feel like payment is more likely to be received if similar yet less hostile message is provided as they still have the option of getting the site build by someone else for a similar price out of spite. (Note the 'Cotton Hill' link on the page is a competitor's site -- that's a pretty nasty thing to link to)