Textbook vs Real
Textbook죄송합니다joe-song-ham-ni-da
Real아 미안미안a mi-an-mi-an
Why Koreans say it this way
죄송합니다 is for serious/formal situations. Between friends: 미안 (sorry) or 미안미안 (sorry sorry, lighter). Doubling words makes them more casual in Korean.
Situation: social