I hear both interchangeably, but I do see a difference. You can have a private official, but you cannot have a private civil servant. Plus official sounds like a boss or a well respected figure who is a professional, now civil servant might invoke that response as well but more than likely not to the same extent. I probably hear official 70% of the time and civil servent 30% the latter being spoken primarily by more educated people.
I had to translate civil servant to two other languages to fully understand what it means. I wonder why this word is so important to Turkish speaking people that they included it. I help my friend with Russian course and it is funny to see how different are contents of both courses. E.g. first lesson in Russian started with words like mother, father. I am level 5 in Turkish already and I have no idea how to say mother in Turkish, though I know civil servant.
I was born in Uk although not been there for 10 years as live in Turkey however I rarely heard Civil Servant used in general speech more just formal speeach and documents and solicitors etc but government official, hospital official, or any official preceded by whatever government type dept seems to be a "memur " in Turkey. I think civil servant although correct is used less and less hope this helps a bit.
https://www.duolingo.com/comment/7738500 This suffix represents the form of to be for "I" or "ben" as in "I am..."
https://www.duolingo.com/comment/7738932 Turkish Grammar Portal
You will need to learn 4-way vowel harmony to know which vowel to use. https://www.duolingo.com/comment/9041808