go back on something
phrasal verb with go verb uk/ɡəʊ/ us/ɡoʊ/ going | went | gone
违背（承诺或协议）;改变（决定）
to fail to keep a promise, or to change a decision or agreement
The government looks likely to go back on its decision to close the mines. 看来政府可能会出尔反尔，推翻原先关闭矿井的决定。
She's gone back on her word and decided not to give me the job after all. 她说话不算话，竟然决定不再给我那个工作了。