Welcome to life in the world of LTC. Most policies reserve the right to raise premiums whenever -- and they do. Increases seem to come higher and faster the older you get until premiums are so high you have to drop coverage about the time you statistically really need the benefits.
I don't have any suggestion for a solution, except carefully read the policy before signing up. Put little faith in what the sales person tells you. Most do not extensively discuss certain "key" facts or what realistic projections of premiums or medical cost increases will be. Years ago some of the reputable large firms issued fixed or limited premium policies but found that they were losing bigtime on the benefits payouts, and to my knowledge stopped writing these types of policies.