Law Office of Vincent Cignarale

I recently was contacted by "The Law Office of Vincent Cignarale". They stated initially on my voicemail that they were from this attorney's office handling a matter they could not disclose, but if I did not contact them within 2 days they would make a decision for me and precede accordingly. When I contacted them, I found that they were actually a collection agency trying to collect on a credit card debt from almost 5 years ago. These people stated that they would make a settlement for 1398.00. I readily agreed, because the Law Office thing scared me, and I really wasn't sure what legal ramifications I could potentially face if I did not agree to a settlement deal. So we made arrangements for the debt to be automatically deducted from my bank account on a specified date. In the meantime, I decide I should have checked into them more, since I have never even received any letters of confirmation of who they are or the debt they were in fact collecting on. I checked my credit report to validate the debt. On my credit report it shows that this debt was written off about 5 years ago in the amount of 572.00 by the original creditor. Then online, I found several statements from consumers like myself that stated this collection agency does not follow the law according to the FTC. So I stopped payment through my bank and contacted them to say until I received a letter of who they are, what they are collecting and for whom, I would not continue with payment. I have received several phone calls from them since asking for my email or fax number and they will get me the letter. My question is.. can they collect more on a debt than the original amount it was written off for? And the statue of limitations is almost up. I read on my credit report that settling this debt, could in fact make my credit score go down, and the only thing that will improve it is if it were paid in full or removed completely..(which will occur in two years) Any info anyone may have is appreciated.