You can't force an update to the hub. As it hasn't updated since 2020 you can only assume the hub is faulty. Call customer services and report the problem and request a replacement hub.
So, last night before I went to bed I factory reset the hub again (this time using the Hub Manager software, rather than pushing the physical reset button). And this morning, I have a dial tone on my phone and the number is all registered!
The firmware is another issue, but I will tackle that one another time...
Thanks everyone for the pointers and the help.
Chris
That is way out of date. Latest version is v44.
Even a spare SH2 I bought 18 months ago had v37 on it initially and updated right away. It is possible that that version is so out of date it's not able to update to the latest version in one go. As Licquorice says, phone CS and request a replacement. If nothing else, being that far out of date could be a security liability.