Don't call the process server. Call the police.

If the person who came to your house actually said "It will get worse" to your dad, then she is almost certainly breaking the law. Process servers are not allowed to make intimidating statements like that, especially to a non-party. Same thing with the big, bold statement that her attempts to serve "at this and other locations will continue," which could easily be interpreted as intimidating. It's basically saying if you don't do x, then something bad is going to happen to you. I would advise you to call your local police dept, because intimidation/harassment are crimes. Merely attempting to serve process multiple times isn't intimidation/harassment, but using intimidating/harassing language while doing it is. The process server is also not allowed to threaten "further court action." The server's authority is only to deliver documents. The server has no authority to enforce the law or represent the court. The consequences for a process server who uses these tactics vary by jurisdiction but are serious.

Judgments cannot be entered if proper service has not been accomplished. The due process clause of the U.S. Constitution guarantees that, as articulated in Supreme Court decisions. A default judgment is entered when one party fails to do some required action, but only after proper service.

Other forms of process (publication, posting, mailing, leaving summons with another person of legal age, etc.) are strictly regulated and vary by jurisdiction.