REFUSE (отказаться): he refused the nomination; he refused my offer of help; she refused my request; she refused permission; she refused them permission to enter; she refused to see him; they refused to discuss the question; he refused to listen (to answer, to go, to co-operate, to help, to obey); I asked him to come, but he refused; you have the right to refuse; they made me an offer I couldn't refuse; I was unable to refuse; she won't refuse him; he refused her nothing; refuse politely (repeatedly, pointedly, categorically, resolutely, flatly, outright, stubbornly).
REJECT (отвергать): he rejected my advice; he rejected their offer of help; he completely rejects this idea; his sons rejected him; she rejected three suitors; they firmly (categorically, flatly, indignantly, unanimously, immediately, consistently) rejected such suggestions; his proposal was rejected as too costly; his first novel was rejected by several publishing companies; damaged goods were rejected by consumers.
DECLINE (polite: отклонить): she declined his invitation; he declined their offer of help; she politely declined to answer his questions; he absolutely declined to discuss his business activity with his parents; they invited her to lunch, but she declined.
Note: Other meanings of DECLINE (идти под уклон, на убыль): the road declines noticeably; his health declined considerably; profits declined by 25%; the market for these products is declining.