"You still haven't answered my question." and "You still didn't answer my question."
Whic one is grammatically correct?

Question

"You still haven't answered my question."   and  "You still didn't answer my question."
Whic one is grammatically correct?

Answer

First one, if you don't express the time.

You still haven't answered my question. (Present perfect is used when we don't express the time, and with words like EVER, NEVER, YET, STILL)

If you expressed the time, like YESTERDAY (Past simple is used for action in the past we know the time for)

You didn't answer my question yesterday.