The “boilerplate” defence to these claims is increasingly being struck out by the courts, and so any defence you use needs to be more specific. You need to give us more background in order to help you here, including posting the original notice and giving us your story.
Of course, the Particulars of Claim from DCB Legal are woeful, and this can be pointed out in your defence, but I suggest this is no longer sufficient as it might once have been.