Read! The mods are declared
I find it hard to believe that (regardless of what power increase be it quoted or actual) that your insurer has not increased your premium at all. I've got years of experience with various cars and numerous mods and the only thing an insurers didn't increase my premium on were interior parts such as buckets harnesses and steering wheel.
I'd wager either you're fibbing or the person on the other end of the phone was a trainee who had no clue. Induction kits, exhaust etc all make the best part of f**k all difference but insurers are always happy to charge you for the pleasure.