I get these calls, no one is on the other line, then they hang up. I have called this number back and it says that this number is no longer in service.

They called twice today. They never gave me their company's name or the name of the caller. They asked for an employee so I transferred them to their extension. They called back saying they got the employee's voicemail & started asking for a few different titles like operations manager & engirneer manager. I asked to be put on their do-no-call list. I'll be reporting them to the FTC too.