My husband and I had a taxi driver refuse to drive us, after a long wait in a cab line after the Berlin Philharmonic. I see online that taxi drivers in Berlin are required to take passengers to their destinations within the municipal limits, unless they're excessively drunk, carrying weapons, etc. That law doesn't seem to help if you can't enforce it in the moment.

Any recommendations on what to do if this happens again?

(His stated reason was that there were older people in line waiting longer than we waited. The people he took looked much younger than we are. We suspect it actually was because he wanted a longer ride/larger fare.)