천만에요 is hardly ever said in conversation and it actually means "Not at all", not "You're welcome.". Some phrases sound OK when written, but they do sound awkward when spoken by someone. For example, 매우(very) is used in formal written Korean, but in spoken Korean, 되게 is used instead. It's important to check if what you learned is *actually* what Korean speakers say in conversation. When someone says "Thank you", we just smile in daily life. When we feel like saying something in response, we say 뭘요 more often than other phrases. 뭘요 means literally "For what", it's implying that you didn't do anything the listener should thank you for.

Considering myself.. I mostly use. 아휴 뭘 이런걸가지고요.. or 별말씀을요... 뭘요 etc and i agree with you i hardly saw some used 천만에요... but it depends on speakers habit so i can not say which one is best good luck

천만에요 is not really used. Check out this video for more detail: https://youtu.be/2RRKNE3Fjzo

Oh, wow, that is really interesting! Just shows how important it is to question what we learn, I think.

What's more interesting is that I learned 천만에요 when I learned "You're welcome.". I haven't ever heard anyone say it, I see it when I watch a foreign movie with Korean captions on TV.