OK - let's get this straight.

There was a "normal" song aout Dublin.

Someone wrote a parody of that song.

You modified that parody to fit your own town.

Someone else recorded and is claiming the song you wrote (with little or no changes).

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Assuming that these are essentially the facts:

Here's basic copyright law in most countries.

A parody that has significant changes from the original song is, in fact, a new set of lyrics and is copyrightable by the writer. (the music isn't, of course, that would be controlled by whomever owns the rights to the music of the original song).

If you have modified a parody and have changed the lyrics significantly enough to be a different song, then you can copyright those lyrics.

If someone has recorded and is selling a song using your lyrics, basically unchanged, then technically, that's probably not legal.

The big question come from the point of whether you can prove those are you lyrics and that you can prove that you wrote them prior to the other person's claim. The easiest way to do this of course is to secure a copyright immediately after writing the song, but most people don't do that.

Have you recorded the song yourself?

Have you performed the song at venues, to a bunch of friends, on the radio, etc. prior to the release date of the offending CD?

If so, you probably have a legal arguement. Contact a lawyer if you think you can prove you wrote the song before the other person says. Yes - even playing the song for a bunch of friends may be enough evidence. They can testify that they were indeed familiar with the song. Bartenders and owners can also do the same.

Good luck.

Blackcatter