If Cignarale's office sent a letter and has proof, it would have to be a signed returned receipt. If you didn't get the letter and you didn't sign a receipt, they don't have proof.
This "firm" is not a real attorney's office. They are a debt collection agency that uses intimidation and bullying tactics to exploit consumers' ingorance of credit and debt collection laws. If they told your mother they were attempting to collect a debt, they've broken the law. If they do not put it in writing, they are breaking the law.
If it makes you feel any better, they've been harassing me for a year and a half via phone. I've asked for it in writing. I've written them certified return receipt letters asking for such. I have never once received anything in writing from the Office of Vincent P. Cignarale. I finally have just decided to ignore their calls.