If you can't find your insurance plan book, I think you have to call your insurance provider. The end of March date and really low deductible and out-of-pocket costs don't sound like anything I have heard of. I had to change plans too, starting January 1, for 10 months; in October I'll be 65 so will have to change again then to Medicare.

They can't change anything without having to send you a new insurance card for the doctors, etc., all of that is coded on there so they can bill properly.