"Du bist somit kein Arzt mehr."
"You are therefore no more a doctor" should also be an accepted translation!
It's a bit too literal, if you look at it you can see that rearranging it to "Therefore, you aren't a doctor anymore" sounds far better as, while your sentence makes sense, nobody would actually say it in English.
It's grammatical in English, and since it's not a course in English or Translation, it's fine if it's too literal for it to feel natural in English.
The point is figuring out what's said in German.
(and it's already accepted BTW)
I translated it as "You are therefore no longer a doctor" and it was accepted. Consider me pleased.