Jessica’s Answer:

My question to you is, did you give them a reason to call you back? FYI: calling to say “I’m available” or “just checking in” doesn’t warrant a return call from someone who has a full schedule. If you called for either of those reasons, consider your objective met; they know you’re available and you’ve officially checked in. Now, if you called for a specific reason like, he/she told you to follow up, or you had a question, wait a week, if it’s not urgent, and follow up again.  THIS TIME, tag on the end that “you know they are very busy, so if you don’t hear back, you’ll try again next week.” Then your call is expected.

My rule of thumb in this business of “sales” AKA “selling yourself” is:
You keep calling until you are told to stop OR until you feel icky about (yes, icky is now officially a business term).

If you are stopping because you feel “icky” leave a closure message along the lines of, “I’ve left 3 messages and I don’t want to be a bother, so I won’t call again. If you do have time to talk in the future, I welcome your call.”

If you have a question, put it in the comment section.
To your success!