Thanks for using Apple Support Communities. I see that the double tap feature are your AirPods don't seem to be working as you'd like. This feature can be very useful when working as it should and I might be able to help get this to do just that. When you say you're trying to get double tap to work, have you adjusted the settings to do something specific or just the default settings of answering and hanging up calls?
What happens if you adjust the settings and attempt to use them as explained in the link below.
Learn more about your AirPods with charging case
Choose a setting that works for you and let me know if that response as it should.
Regards.