keep at

English

keep at (third-person singular simple present keeps at, present participle keeping at, simple past and past participle kept at)

(transitive) To persist in.
Learning a new language is hard, but if you keep at it, you'll get better.
(transitive) To constrain (a person) to continue doing (a task).
If he doesn't get back to you right away, just keep at him and eventually you'll get an answer.