The PPoE should be your primary VZ username. The password field just needs to have something in it. It can be nonsense.
The all wont "sync" One is for the router logon. One is for the router to connect to VZ (PPoE) and the other (which can be the same username as PPoE) is to access your account and such on the web (VOL) As long as the username you connect to the VZ websites is the same as your primary (first one set up w/ VZ) it should work. If the username for PPoE on the old router worked it should still work.
It sounds like one of the combos should have worked.
The only think I can think of is that it is trying to grab the same wan IP as the previous router. Since it is PPoE this should not happen as it almost always releases when you disconnect.
That's all I got
Call VZ if you have to.