iOS 11 moved the carrier related menu service options from within the Phone control panel.
now its found within the Cellular control panel. under Carrier Services.
however, this control panel, and what is contained in it is totally driven on a carrier by carrier basis.
what is in your Carrier Services (or even it appears at all) can and is very different when it appears in other carriers' phones.
its found in Cellular/Carrier Services.
anyway, look in that control panel.
it lists any/all services that your carrier tells apple it wants you to be able to control directly, like turning on call waiting, or, call forwarding, etc.
your problem sounds like it might be able to be solved within this panel.
the other thing that would definitely help is to visit a different Verizon store in person where you might find an experienced representative who would definitely be familiar with iOS 11.