Design low pass filter with a given transfer function

I must design a low-pass filter with a given transfer function in z-domain:

H(z) = (1-z^(-6))^2 / (1-z^(-1))^2

Considering the x signal (1x2000) I want to filter, i wrote

N = 2000;
h1 = zeros(1,N);
%
% a. Low-Pass Filter
for i = 1:N
    if (i == 1)
        h1(1) = 1;
        a1(1) = 1;
        b1(1) = 1;
    else
    if (i == 2)
        h1(2) = 1/(1-2*x(1));
        b1(2) = 1;
        a1(2) = 1-2*x(1);
    else
    if ((i == 3) || (i == 4) || (i == 5) || (i == 6))
        h1(i) = 1/(1+x(i-2)-2*(x(i-1)));
        b1(i) = 1;
        a1(i) = (1+x(i-2)-2*(x(i-1)));
    else
    if ((i == 7) || (i == 8) || (i == 9) || (i == 10) || (i == 11) || (i == 12))
        h1(i) = ((1-2*x(i-6)))/(1+(x(i-2))-2*(x(i-1)));
        b1(i) = (1-2*x(i-6));
        a1(i) = (1+(x(i-2))-2*(x(i-1)));
    else
    h1(i) = ((1+(x(i-12))-2*(x(i-6))))/(1+(x(i-2))-2*x(i-1));
    b1(i) = ((1+(x(i-12))-2*(x(i-6))));
    a1(i) = (1+(x(i-2))-2*x(i-1));
    end
    end
    end
    end
end
figure,
freqz(b1,a1,512,fc);
y = filter(b1,a1,x);

Is it correct? I don't think so because the plot it is a mess and definitively not a low-pass! What is it wrong?