It could be that you are a witness to some event that they represent someone else for, they could represent a creditor of yours, or many, many, many other reasons.
The most obvious reason to interview with law enforcement is that the defendant wants some sort of deal. Whether that is a plea bargain, immunity, or even not being charged, the defendant is hoping to show the prosecutor that they are either innocent or have some important information to offer.
There are several ways for criminal defendants to convince a prosecutor to drop their charges. They can present exculpatory evidence, complete a pretrial diversion program, agree to testify against another defendant, take a plea deal, or show that their rights were violated by the police.
Defendants are advised not to speak with prosecutors. There is no specific rule that prohibits a defendant in a criminal case from speaking directly with the district attorney in an attempt to negotiate a resolution of the charges.
In short, lawyers are people, but they don't actually have any authority. If there really is a problem, you'll hear from them again; lawyers are tenacious if nothing else.
A call from one with no message is probably a wrong number if it is actually from a law firm. Anything serious and you will get a letter, another phone call with a message, or an in person visit. So, don't worry about it. It's most likely a spam phone call with a fake caller ID. 10 years ago.
Those who address these investigations or actions properly have the best chance of obtaining a positive outcome. An attorney general investigation can come in many forms, from a simple letter to a Civil Investigative Demand (“CID”) or subpoena.
If a lawsuit has been commenced, the goal is to get the quickest, most cost effective and painless resolution.