When you purchase a policy through Grand Circle, you're actually purchasing TWO policies. The first policy is a 'Cancel For Any Reason Policy( if you can properly call it a policy )," and that's underwritten by Grand Circle. that's separate and apart from the policy marketed by Trip Mate, which includes such things as medical coverage, baggage insurance, trip delay, etc. Trip Mate, not one of the companies which offer better coverage for the price, and service, is, however, like all the rest of the companies, in that medical expenses must occur withing the dates of your trip. So they are correct in denying a claim for expenses incurred AFTER you arrive home. That is made quite clear in the policy do***ents you received, and which are published in the Grand circle handbook. If you read it when you received it, you could have questioned the aparent contradiction between what Grand Circle stated in their marketing information, and what the actual policy said. Unfortunately, it's not a good time to clarify the contradiction after the fact. Whether or not Grand Circle resolves this issue to the OP's satiafaction remains to be seen; we wish the OP luck.
But this brings up another point: Purchasing travel insurance in the first place. We recommend shopping your insurance from various sources BEFORE you book a trip. In that way, you will be prepared to purchase your policy immediately after you book your trip. You need to do this because of the way in which "pre-existing conditions" are defined by most companies. We've written on this topic many times previously, and have given various sources tp peruse. They can be searched in this forum.
As a final comment: We've never purchased the insurance offered by Grand Circle. We've always found we can do better, either getting better coverage which may be needed for some trips at a better price, or both. Travel Gurad was mentioned by a previous poster, and we have found that they usually( but not always ) are the best. But that's AFTER we shop each trip.