It's difficult to advise without seeing your feedback or work.
Was the feedback clear? Did the tutor explain what you needed to achieve a distinction?
For example, in one of my assignments, I received a "merit" for communication because my referencing did not follow Harvard style.
If you are unsure how to improve your work, you have the right to ask for clarification. Tutors are there to help you learn how to complete assignments well, not to fail you.
If you disagree with your grades, you can always appeal—check the policy. I once appealed a merit, and it was changed to a distinction.
Don't despair about your offers. Would you still be able to meet any of them if you achieve distinctions in your remaining assignments?
If so, I’d be happy to share some tips on how to achieve a distinction or at least what has helped me.
And yes, I agree—the grade descriptors are useless!