Global Services Scam - False Debt Collection / Personal Information Gathering Unknown Nationwide

They have my full, legal name and last 4 of my social security number. Wanted me to verify the rest of it as well as bank account information. The did "sound" official but something seemed "off" and when I questioned who they were they became rude. Said they were collection company for a payday loan and threw in a bunch of threats. I have NEVER used a payday loan. When I said so, they hung up on me. I checked all credit reports to ensure nobody had taken one in my name... They have since called every phone number ever associated with me. My best guess is that they pull some sort of background report(s) and use them (with just enough info) to trick people into paying off collection debt that they dont have -or- Use it to trick people into filling in enough of the blanks that they can then use the info to create false identity/fraud.