I think that the idea is that you treat it like a sudoku, working your way around the board.
Your answers for 9A, 12A , 20A and 11D are correct.
Your two options for 16D are correct, but it’s tied to 15D. This is where you probably have to take a leap and see where it takes you. 15D is unlikely to be EXACTLY the same as 16D. Therefore we could assume that 16D is 91, and 15D is 13 (it has to be a two-digit number). Which then tells you 14A (2197)…
17A can be either 89 or 83, which affects 4A.
I’ll come back to this later, but you might be able to solve it from there