The two pieces in question:
Loyal Moon: http://www.poemranker.com/poem-details.jsp?id=67991
Unloyal Poon: http://www.poemranker.com/poem-details.jsp?id=68228
Is that poem your only offering of evidence? Yes, such rewriting of your piece could be construed as rude. It was probably intended to both be offensive, and if you cared to puzzle it out, instructional. I see no grounds for harassment, and it is by no means plagiarism.
As far as the multiple accounts, yes, people may create as many accounts as they wish. It is not encouraged, but there is little to be done about it.
If you wish to leave poemranker, simply delete your poems and information and it will be as good as done.