I've received this call a few times this week and when I called it back it appears to be a Verizon Wireless msg center. It doesn't give me the option to reach anyone, just an automated message asking for a reference number. No idea why I'm getting these calls and I obviously do not have a reference number. No one's ever left a message.
Yes, definitely Verizon Wireless calling about a past due balance. It does seem to take them awhile to catch up after you've made a payment. I just got a call from them even though I paid online a couple of days ago.