Your dimensions don't work. A*B is going to be 3x1. You can't multiply this by a 3xN matrix.
That being said, suppose you did have dimensions that did work for A*B. Then you don't need to split anything up for the multiply. You can just do A*B*C directly and then pick off the columns of the result that you want. E.g., suppose we have the simpler problem below
A is 3x3
C is 3x12
and we want A multiplied by individual 3x3 parts of C. Then instead of doing these individual matrix multipies
D1 = A*C(:,1:3)
D2 = A*C(:,4:6)
D3 = A*C(:,7:9)
D4 = A*C(:,10:12)
You can just do this all in one fell swoop
D = A*C
and then reshape it for convenience
D = reshape(D,3,3,)
Then you can pick off D(:,;1), D(:,:,2), etc. for your results.