I also have ReSound hearing aids and it drove me crazy that the default was to stream everything to the hearing aids. However, I found a solution I am comfortable with without having to turn Bluetooth off. I am in Canada and that might matter. When I got these hearing aids I also got an App that I can control them with as well as create new sound levels depending upon my circumstance. I can also temporarily adjust the default sound levels that were added to my hearing aids as a result of my hearing test.
Once the App was installed on my iPhone it also added Accessibility controls here:
Settings → Accessibility → Hearing Devices → Audio Routing
I have Audio Routing set to “Never Hearing Devices” for the entries for Call Audio and Media Audio.
Hope this helps but if I have misunderstood then my apologies.