Calling senators--I need your suggestions. What if you can't get through to leave a message?

I was unable to get through to Lindsey Graham's office last Thursday, and this morning.
I know the office is closed now, but you'd at least think I could leave a message.

No dice, I got "sorry, the mailbox is full." (Same as I got last Thursday.)

Well, this morning I called the upstate office--Mailbox full. Same with Midlands office.

I send him two emails but I WANT TO LEAVE HIM A PHONE MESSAGE. It's very frustrating.
Don't the staff ever clear out the mailboxes? Or is this a way of saying they don't want to be
bothered?

"Call your Senator/Congressperson" --it sounds so easy, doesn't it?

But if you can't let him/her know what you think, what use is that?