It's one of those stupid collectors that uses the scare tactics of serving you with a summons. I don't know what company it is. When I called the number back it didn't give a company name.
This is a collection agency posing as a law office threatening to serve you papers for a civil suit. I told them to send something to me in writing, they kept trying to get me to give them my social security number over the phone.
These people call, never leave a message. They use a local number, so the call seems more legitimate. I never answer a number that I don't recognize and has no caller ID. If it's legit, they can leave a message.