An accent tells people where you learned to talk, not how well you learned to think.

One of those is geography and the other is ability, and they have nothing to do with each other. Anybody who hears a few vowels and adjusts their estimate of your intelligence has made a mistake about information, not a discovery about you. The confusion is very common and still a confusion.

Keep speaking the way you speak, particularly in rooms where you suspect it is being counted against you. Let the content do the arguing: ask the sharp question, give the good answer. When somebody slows down or simplifies at you, carry on at your own pace instead of shrinking to fit their assumption.