How can I plot the amplitude and phase responses of a Cascaded Integrated Comb filter?

I'm trying to plot the amplitude and phase responses of a Cascaded Integrated Comb filter

But I don't get the right Sinc function in the amplitude response, any idea? Here is the transfer function in discrete domain.

and Here is my code

clear all 
close all 
clc

omg = -10:0.01:10;
N = 3;
M = 1;
R = 2;

n = [-1 zeros(M*R-1,1) 1];
d= [-1 1];
num = [1];
den = [1];

for i = 1:N
    num = conv(num,n);
    den = conv(den,d);
end

H = freqs(num,den,omg);
figure(1)
plot(omg,abs(H))
figure(2)
plot(omg,angle(H))