I Closed the Fraud Account Opened in My Name but Still Getting Calls

[frustrated_non_customer]

I had a Verizon account fraudulently opened in my name 1-2 months ago. I am not a Verizon customer. 

As soon as I got the paper bill mailed to me, I called Verizon, spoke with the Fraud department, and the account was closed. I was assured that I would owe nothing on the account as it was flagged as fraudulent.

Then I got a bill for the balance, called Verizon fraud department again, and was assured that it was just a timing issue and the balance was gone.

Fast-forward a couple weeks later, and now I'm getting automated calls from "Verizon Financial Services" saying I owe a past due amount of ~$500 from a phone number with a 256 area code. It provides a callback number and a reference number to give. 

I called Verizon fraud team again, who once again assured me that I am not liable for the balance and I can ignore the calls.

My question is this: why am I still getting these calls?  I've probably gotten 7 calls from "Verzion Financial Services" about the past due amount. Are they spam or are they legitimate?

This balance should have been wiped away and nothing in the system should show a past due amount. I am worried that Verizon hasn't done something correctly and this past due amount is going to sent to collections where I have to deal with that headache for an issue that should already be resolved. 

Please advise on this can be fixed as soon as possible.