called them back, but call "could not be completed as dialed"

They called but did not leave a message on machine

Call display on my phone says name of caller is 407-000-2312, and the phone number of caller is 1-407-000-2312.  Who is this, and what is the objective of the caller?  Is it some kind of hack attemp on my telephone line?  How can I deal with this best?  Thanks!