When asked about the make-up exam, the teacher never replied.

The teacher was very busy and didn't receive the news.

1. The teacher has a lot of things to deal with and can't reply to the information in time. You can try sending the message again, or contact again when the teacher is free.

Sometimes, for various reasons, the teacher didn't receive the message. You can confirm whether the message you sent was successful or resend it by other means.