I can't say whether you would be contractually obligated. It's a very good idea to complete the survey and send it in as the carrier may put claims processing on hold for you until it receives your updated information. This means your providers won't get paid and when they don't get paid it's you they will be looking for.The insurance company sends these questionnaires because when someone has more than one form of insurance the different carriers take on roles u2022 primary, secondary, tertiary, etc. The primary carrier pays first according to the terms of the policy. The secondary company will pay second, but they will only consider what's left after the primary pays.For example, let's say your ER visit was $2000. Your deductible is $1000 with the primary carrier and the primary insurance pays $1000.Your deductible with the secondary insurance is only $500. The secondary carrier is now looking at a bill for $1000. They pay $500.In the end, you paid $500, primary paid $1000, and secondary paid $500.If you only gave the provider information on your secondary insurance, they would be billed that while $2022 (as the ER wouldn't know about your other coverage). The secondary carrier, knowing they're second, will insist it's sent to the primary carrier for payment first.If they don't know there's a primary carrier, this becomes a very different financial situation for them u2022 instead of $500, they pay $1500! That's your full bill less the $500 you pay out of pocket.Not knowing about the primary carrier just cost the secondary insurance an additional $1000.It's for this reason that they keep sending you questionnaires, and for this reason that they could hold off on processing your claims if you don't respond. In the end their goal is to save as much money as possible by making sure that they don't pay anything for which they aren't liable.