お世話になりました
おせわになりました · osewaninarimashita · JLPT N2 · noun
care
お世話 = looking after + になりました = has become: I've been looked after
世話 means looking after or taking care of someone, and お adds politeness. になりました turns it into a past state, so the phrase says you have been under someone's care. It is used to thank someone after they have helped you.