If the activity has a tick and is completed, but in the grade area you can only see a hyphen symbol: ‘-‘ this means you got all of the activities you attempted wrong and did not achieve a grade.
Therefore, the hyphen ‘-‘ means zero ‘0’ points.
You could go back into the activity to make sure you did not forget to complete any tasks, complete those tasks, submit the activity, and see if you get a grade.
This video demonstrates how to complete activities:
href="https://media.intostudy.com/video/upload/v1593188232/Central%20video%20gallery%20linked%20to%20VLEs/Student%20Videos/How%20to%20complete%20your%20elearning%20activities.mp4" rel="noopener noreferrer" target="_blank">https://media.intostudy.com/video/upload/v1593188232/Central%20video%20gallery%20linked%20to%20VLEs/Student%20Videos/How%20to%20complete%20your%20elearning%20activities.mp4
If you are still unhappy, speak to your teacher and explain that you are unhappy with your grade. Your teacher will then take note of this and talk to you directly.