I've never known any property have a built-in IHD and searching the Certified Products List over on the ZigBee Alliance website hasn't produced any results either. They've always been portable for as long as I can remember.
With that being said, I can already diagnose a lot of potential issues. My first guess is that this is a read schedule issue so I'll summon @
PeterT_EONNext to take a look. As for the firmware, it's impossible to be outdated unless the meters aren't communicating at all. Automatic firmware updates are always enabled by default and the meters will process them when they become available. It can take a few weeks in some cases for such updates to rollout though and the meters will restart/reboot as part of the firmware update process. There's nothing you need to do - and nothing you can do - in order to force an update through. If it keeps failing, the supplier is notified.
As for the IHD, you can't just buy these from anywhere. If you have SMETS2 meters, your best bet is the
ivie Bud, while for SMETS1 you'll want the SMETS1 variant of the
Hildebrand Glow, assuming it ever comes back into stock. E.On Next has been very... Difficult... About supplying new IHDs and their default choice of the IHDL SmartView 2 is a
horrible IHD.
If you're unsure what meters you have, I can identify them for you if you post photos.