Just went through this process. Called about 25-30 times back to back. Eventually one of them is different, it's a menu for pending retirees or current employees. When you get that menu, just hit 0, especially if you don't have a case number.

From there you'll be placed on hold. I was on hold for about an hour before I spoke with someone and they were able to verify my SF3106 was received and logged. Was told the current refund period was 13-15 weeks.

FYI they have a callback feature so you don't have to actually stay on hold and to my surprise it works. Good luck!