I have a little update. After few months they sent another letter. very brief stating :
We refer to previous correspondence regarding infringement of our client's copyright in work ...
We are currently awaiting instructions from our client in relation to the various points you have raised in your last letter. Once we have our cleint's instruction we shall revert back to you.
In the meantime, we expressly reserve all our client's rights.
I believe there's no point to write back to them right? The letter is from 13/03/09. I sent mine like 3-4 months ago.. That was quick