What is the right problem that should be solved here?
People shouldn't really be walking around in public with ANC on. It's not safe. Not a simple problem to solve except maybe to inform people better upon buying/setting up ANC-enabled devices.
Fines. No one should cross roads/paths randomly, with or without headphones.
One large fine, and people will learn.
Better segregation of cyclists and pedestrians into their own spaces. The bell shouldn't be something that you use regularly.