Answer:
By imitating the cry for help of Jonathan's family as a way of mocking them.
Step-by-step explanation:
Chinua Achebe's short story "Civil Peace" is mainly around the Nigerian Civil War and its effects on the people. The 'civil peace' that ensued this war was something that Achebe wants to greatly stress on in this story.
Jonathan Ewegbu was the protagonist of the story. He had been doing some small business and getting a good sum of money inflow. One night, robbers came to his house demanding he give them 100 pounds. It was this night of robbery that the question is asking about. When the family began yelling and shouting for help, the robbers began imitating them, shouting like they did. They mocked them in attempting to attract some sort of help.