I work in car insurance all I can say is if you have proof of your 27 years ncb and the date on the letter is less than two years old from when you took your new insurance out, and you have your proof of ncb from aviva. I would ring up your current insurer at the service department and ask to speak to a manager I would then say that you have both documents stating your real ncb and the letter from aviva and that you want your bigger discount applied. Are max ncb is 9 years but that doesent mean you should loose the rest. I would also maybe get them to rin aviva to confirm you have had no accidents in the time you were with aviva and that your full 27 years ncb do still count.