Viet lai theo 2 cach It wasn't necessary for them to call for help after all.

→They didn’t need to call for help after all. ( chủ ngữ chỉ người+didn't +need to : ai đó không cần làm gì) 

→ They didn’t have to call for help after all.( didn't + have to có nghĩa là không phải làm gì)