Did Verizon say specifically what triggered the fraud alert on their end? It didn't have anything to do with a credit card or bank account?
I had a situation with a another mobile carrier that couldn't apply an auto monthly payment to my credit card. Neither could Paypal, but my card worked fine for local charges. Turns out my bank had put a hold on online charges due to what they deemed was a suspicious amount charged from Paypal. Was less than $20. that I had made for an Ebay purchase. However, the bank never called me to verify. Luckily, they have 24 hour customer service in the U.S., and the hold was quickly removed.
Unfortunately, due to so much electronic fraud these days, it doesn't take much to trigger an alert. A situation that can be frustrating, and inconvenient when it happens.