its basically a solenoid for each cam, operated by th ecu, which reroute the oil pressure from one set of chambers in the sprocket to the other, forcing the cam one way or the other. But you have changed the full VVT unit haven't you?!
or are they filling you full of sh**?
if your vvt unit is new, and the sprockets are new, then thats the entire system changed over, so then i suppose it could only be either a weak signal from the ecu thats not operating the solenoid properly, or poor oil pressure?
good work mate.