As a last resort try a different router perhaps? (put the Virgin router in bridge mode and connect the new router to it)
Things like wifi doorbells are designed to be very easy to setup and you shouldn't
really have to play around with port settings on the router to make it work. Otherwise it would scare off 99% of potential buyers. FWIW I have the Skybell (one of the first wifi doorbells to be released) and it was an absolute doddle to setup - i certainly didn't have to faff around with port settings in order to get it working.
FluidOne FTTPoD 330/30
Edited by baby_frogmella (Tue 30-Oct-18 22:38:58)