Firstly, we say xiexie qing bukeqi just like you English speakers say thanks please and you are welcome, theae words are used to show your manners. You can say xiexie to any person who helps you, of course includes the waiter and waitresses.They served you,you say xiexie. We say qing just like you say please.You ask a question, and say please and the end of the sentence.We say qing at the beginning of a sentence---Qing wen.......? We say bukeqi when you recieve a thanks. But duibuqi is not like sorry exactly.when you do something wrong, you say duibuqi, like sorry.You say I'm sorry for that to describe you are sad to hear that. While you can't use duibuqi then. You can say wo hen bao qian instead duibuqi. When you need someone's attention, you say excuse me, in Chinese we sometimes use dubuqi. For instance,duibuqi, xie guo yi xia.duibuqi ,rang wo xian lai ke yi ma? Got it? Since you said xiexie .Then I should say Bukeqi, zhu hao.