The same thing has happened to me also. My old IHD has power supply issues, so I requested a new IHD. Took a couple of months but it arrived. Followed instructions and nothing. Called Utilita, was told to leave it without power and without the batteries on top of the meter for 24hrs. (Which is insane how is it supposed to pair with the meter without power?) But I did as they asked. Nope didn't work, I called Utilita again to be told my meters are faulty (both of them at the same time?) and they are sending an engineer out in three weeks.
CS agent wouldn't listen to me, when I asked if the new display could be faulty.
Bonkers.