call a lawyer - then find out if there is a statue of limitations on medical.
6 years later and no bills and they are now coming after you for them? Was it on-going medical treatment during that timeframe from insurance companies or something?
I do not believe they can come after you all these years later w/out billing you or notifying you unless you've been being seen for continual treatment all this time and its been in a constant insurance claim type of situation.
Lawyer is whats needed, one that specializes in medical - and fast. Sounds to me like someone went through their accounts and said "oh look - someone owes us money from years ago.. lets collect now" and is using scare tactics to get it. They cannot go into any bank account without notification, especially years later and without giving you proper notice/attempts to pay first and foremost, be it through a payment plan or whatever. Illegal as all all get-out.
And so far as collection agency's go - some of them are scum of the earth and use some pretty bad methods/means to get people to pay their bills that are illegal and border on questionable ethics at best. If they keep calling your mom, she can tell them to quit harrassing her (tell her to get their name, number, extension, company, etc) and if they call her again, she will report them for harrassment. Look up the law (there is one out there) for this type of situation and they must abide by it or face very stiff penalities. This is why its best to get a lawyer involved because they will handle it all. Also, if they DO keep calling after you tell them not to (and please, learn the law and code, and cite it back to them) and leave you msgs on your machine - RECORD THE MESSAGES and keep them...you can use them in court because they knowingly left them on a recorder (they are admissable). Judges hate collection agents that abuse what they do - trust me. We went through this about 15 years ago and we had our entire medical bill thrown out of court ....just for this reason.