I think you've forgotten to reduce individual sums mod 9 (i.e., by adding digits) before adding them up. 5658 4612 3826 9730 [original number] 10 6 10 8

I think you've forgotten to reduce individual sums mod 9 (i.e., by adding digits) before adding them up. 5658 4612 3826 9730 [original number] 10 6 10 8 8 6 2 2 6 8 4 6 18 7 6 0 [double alternate digits] 1 6 1 8 8 6 2 2 6 8 4 6 9 7 6 0 [digit sums] 16 18 24 22 [sums of groups] 80 [overall sum] Of course you don't need to bother with the sums-of-groups step; that was just to make it easier for you to notice if I made any mistakes.