If the virus was on your phone, how are you blaming Verizon? If you allowed a virus to remain on your phone for that long, I would say that 1. Data overage from Verizon might be the least of your worries, if you do any banking or use a syncing calendar or anything like that on your phone; 2. Get a virus protector on your phone. I use Lookout, and I use the free version, and have had zero issues since my first smartphone in 2012.
Verizon can't tell if the data use is from a virus or hacker. It is your responsibility to protect your phone (thereby protecting YOUR sensitive information), and yours alone.