When did the collection agency first contact you regarding the debt? Also, has the statute of limitations expired on the lawful collection of the debt as well? You can still send an FDCPA validation letter, but if it is sent after the initial 30 days from the first written notice that was sent to you by the collection agency, AFAIK you will only be limited to being able to ask them to verify their legal ability to collect the debt (statute of limitations and so forth).
Also, the collection agency (IIRC) is required by law to send you a written collections notice. If he refuses to, contact an attorney and prepare to file suit against them. You'll also want to file a formal complaint against the collection agency with the Federal Trade Commission (FTC), which has jurisdiction over FDCPA, FCRA and CPA (that's the Consumer Protection Act, not a certified public accountant) law enforcement.
There was a recent amendment made to the FDCPA (which was signed into law by the President last month) stating that collection agencies may continue their collection attempts against you during the initial 30 day period as long as A.) you have not sent them an FDCPA validation request letter, and B.) the collection attempts do not otherwise violate the FDCPA.
Of course, since IANAL (I am not a lawyer), this is about as much as I can tell you. From here on in, you'll have to find a lawyer that specializes in debt collection abuse cases (you want to hire an attorney that represents CONSUMERS, not collection agencies) to help you, since everything beyond what I have posted here (in YOUR particular case) could be misconstrued as giving legal advice, which I am of course not qualified nor licensed to do.