Checking my last day of health coverage

I was told my coverage ends on my last day, but the letter says the end of the month. There are 18 people counting on me, so I am trying to be careful. I have an appointment next week. What should I do about appointments?

I moved my appointments earlier while coverage was active. It saved me a bill.

Ask HR to confirm the exact date in writing. I also called the insurance company to double-check.