Continue. Do not give up. Many many people are just looking for someone else to do it first; it emboldens and encourages them; go without the mask. As often as possible.
Say “Thank you, I’m fine.” if or when they hassle, say it louder. Multiple times.
The final time, shout “THANK YOU, KAREN, I’M FINE.”
...or... ...a simple F O when walking past is sufficient to!