they really have you when there is a pre-exisitng condition don't they
. HP put up my premiums nearly 100% (but the benefits had also increased). i finished up downgrading to silver - Kira has a pre-existing ear condition so it would be difficult to change insurers without loosing ear cover.
if i read your post right it seems to revolved around the non-compliance of the vets to the information request (i guess this was the 12 month history). As Dylan as been covered by the insurance for 5 years, i find it strange they want this now, but if this is what is required to get the bill paid then i think i would get the vet to provide it. Alternatively, rather than you acting as go between ask your vet to contact HP directly to see what need to be done to get it paid.
good luck