go back on
US
UK go back on a promise v expr: (break your word)
SC 不遵守诺言，打破承诺 bù zūn shǒu nuò yán，dǎ pò chéng nuò
SC 背信弃义 bèi xìn qì yì
I can't believe that you, my own brother, would go back on your promise to loan me the money.
go back on your word v expr: (not keep a promise)
SC 食言 shí yán
SC 说话不算话
Janice went back on her word to help me with the cooking.