I agree that sounds like a blocked port. But I don't know which one it requires. The built-in Port Configuration Test won't help much as it's designed for US TiVos and often fails even on a fully-working setup.
This page may give you some clues, but again it is intended for the US market and isn't necessarily correct for VM boxes:
https://support.tivo.com/articles/Tr...ng-my-TiVo-DVR