Not uncommon for InsCos to try and duck a claim of course. It boils down to what you told them at inception - whoch may be tricky to prove if done online. They'll almost certainly have a get-out-of-jail card in that it is the policy holder's responsibility to check the data at the outset.
AFAIK Data tag is 'just' a marker for individual parts on a vehicle? If someone typed in Datatag in a free-format cell at inception - I don't think the insco are expected to know every brand of immobiliser so it's back to what was input at the outset...........