Doctor doesn’t tell people what they owe, it’s usually the billing department or their office manager who does (at least in the US)
Source: This was my job after college. I worked for a mental hospital, and it was my job to tell people how much their hospital stay was going to cost. A lot of the time, these patients were hospitalized because they’ve tried to commit suicide. So glad I don’t work there anymore.
For some of them, I was able to sign them up for Medicaid, so their stay could be covered. Lots of people set up payment plans. For the people who didn’t/couldn’t pay, we would send them to collections. My hospital very, very rarely wrote anyone off. IIRC the cost for one night without insurance was around $4k.