One thing you may want to do is disable the UPnP feature in your router, if it's turned on. Although on Consoles this increases your NAT Type to Moderate NAT or NAT Type 2, it helps to lessen the number of connections you're making to other peers in a lobby or game. Voice calls will still be transmitted through "Peer to Peer" unless the console has gained an ability to use a Relay server. Relay servers are something to look into.
Something else which helps is ensuring your Public IP isn't allowing pings. By default, the FiOS routers should be set with the Firewall set to "Low" which will stop ICMP pings.
Beyond that, if you know who is attacking, report them to the online service (XBL, PSN, Steam, etc) for initiating denial of service attacks. This goes against laws like The Computer Fraud and Abuse Act, and is also against the Terms of Service of any reputable ISP, whether it's Verizon, Xfinity, AT&T, Spectrum, etc. Players engaging in activities like that can certainly get their Internet access disconnected, and can also get their accounts disabled or banned. It doesn't matter how good they are in Call of Duty.
As for changing the FiOS IP address, you would need to change the MAC Address that Verizon sees to get a different IP address, or you'll need to leave your router off for several hours and pray someone else claims your former IP address. Generally, changing IP addresses just shifts the problem to someone else if it's a sustained attack, and really shouldn't be done (IMO).