Sirs,
This is to inform you that I am canceling my (pet’s) insurance policy:
My cat, Chanel, has a congenital blood condition that affects her health in the following way: it makes it impossible for her to be insured by the terms of your endorsement.
Note: this was sent to the insurance company in an actual envelope, snail mail. The company called to determine 'what up.' I felt that I was convincing during that phone call, and that my point had been well taken. The company promptly…sent a bill for the next year's coverage!
(Which should surprise no one! – The surprising part is that I'm such a doofus as to pay any attention to the letter of the policy.)