Welcome bcsteve and yikes!
So at this point, someone is using your phone with your google play account to download apps correct? I hope you dis-associated any credit card with also?
I really don't know what to tell you as you have done alot of research and investigation yourself about it
I was trying to think of something else that can be done if I was in your situation, other than start deleting apps from Play
I hope you get this resolved or someone else can offer some advice