"Thank you. You're welcome."
Many Korean textbooks introduce 천만에요 [cheon-ma-nae-yo] as an expression that you can use when someone says “Thank you.” to you. So, it can be translated as “You are welcome.” or “Don’t mention it.” in English. Here, 천만 literally means ten million, which is basically a very large number. In the past, when people were talking about something unlikely to happen, they used this word “천만” and here, -에 means “in” or “at” referring to a location and “요” makes the sentence 존댓말, the polite form. So all toghether, it means “even in thousands or tens of thousands of situations like this, you don’t have to say “Thanks” to me.” In everyday conversations in modern-day Korean, however, the expression 아니에요 [a-ni-e-yo] is more commonly used than 천만에요. You can still hear 천만에요 being used in some TV dramas, movies or in books, but not many people actually “say” this in their daily conversations.
No they don't. Like I've been living here in korea talking to people in korean everyday (literally) and I have yet to hear that phrase. Usually it's 아니요, 네, or 괜찮아요. If anything.