By law, when you buy a Medigap policy, you have a 30-day “free look” or trial period. If you change your mind within 30 days of the day your policy started, you can cancel it and get a refund.
If you are switching Medigap plans, do not cancel your first policy until after your free look period is up. You may have to pay two premiums for 1 month. But you will be able to change back to your first plan if you need to.