If your teacher tells you he has not received your assignment, it could be because you did not submit it correctly. When you complete an assignment, you will first see this message:

If you close the window here, your teacher will not receive the assignment. You must click on "Submit". Then, you will see this confirmation message.

Your assignment will no longer appear in the "Active" category but in "Submitted" and your teacher will be able to see and mark it.