Can't Setup New RBK853 / RBR850 with Virgin Media Hub 4

I recently bought a refurbished RBK853, so 1 router with 2 satelittes. I am based in the UK (London), and currently signed up with Virgin Media 1gig broadband, delivered via their Hub 4 router.

I've tried multiple times, in differing orders, but essentially, I have put the Virgin router into modem mode, left for 5 minutes, restarted, left for 5 minutes, connected the Orbi router, with 2 different CAT6 cables incase there was a problem with 1 of them, via the yellow WAN port on the Orbi router, and have tried using ports 1, 2, 3 and 4 on the Virgin router, done the setup in the app, each time, all works fine and finds the satellites, until the end where it can't find/connect to network Orbi29, and that network is not shown in my wifi connection options on my phone or laptop.

I then tried connecting the Orbi router to the Virgin router whilst it was still in router mode and then connected to Orbi router via ethernet from my laptop. I'm asked for a username and password, and have tried Admin / Password which doesnt work. Doing the password reset doesnt work as it asks me for security questions, which I presume have been setup by previous owners?

I have done a factory reset via the reset pin on the Orbi router and both satellites, correctly getting the flashing amber lights on each one to indicate factory reset has happened.

Can anyone help advise how I can log into the Orbi as admin and/or can anyone suggest why I have been trying for 2 days to connect without success considering it seems like it's such an easy process to put the existing router into modem mode and then connect the Orbi router? Pulling my hair out a little bit as this is an extremely expensive piece of kit!

Any help or suggestions greatly appreciated. 

Thanks

Chris