The 30 days is not a " cooling off" period, If you HAD sent them a validation request within the 30 days, they violated the law. If you haven't. well, they can still sue you, but your chance to get validation hs not expired and if they ignore that they do so at their peril.
If the debt collector failed to explain that the lawsuit does not diminish the 30 days validation period, then the lawsuit overshadows the 30 day notice and so may be a violation of the Fair Debt Collection Practices Act (FDCPA). I have written extensively about the FDCPA here: http://nahoumlaw.com/tag/fdcpa/
You should consult with a consumer attorney experienced in the FDCPA.
ATTORNEY ADVERTISING: Past performance is no guarantee of future results. The foregoing statements and links are made available by the lawyer or law firm publisher for educational purposes only as well as to give you general information and a general understanding of the law, not to provide specific legal advice. You understand that there is no attorney client relationship between you and the Law Offices of Robert J. Nahoum, P.C.. The foregoing statements and links should not be used as a substitute for competent legal advice from a licensed professional attorney in your state.