Designing a multi-band FIR filter on MATLAB
According to your filter equations, your polynomials for $b1$, $b2$ and $a$ should only contain 1, zeros and -1. Your don't need to evaluate the last coefficient (num_exp, and others) at the complex exponential - That is done inside the freqz()
Take a look at this example here
So you should have:
a=[1, -1]
b1 = [1, 0, 0, ..., 0, -1]
b2 = [1, 0, 0, ..., 0, -1]

So $a$, $b1$, $b2$ contain the coefficients of the $z^{-n}$ terms.