Double integral by composite Simpson rule

Helo :)

I need to write Composite Simpson rule for double integration od values x and y. I have a function , where lower limit for x is and upper is and lower limit for y is and upper limit for y is , and and . So far I have this code, but it is for one value and i dont know how to fix it. I wanna first write a code for this rule and than make calculation for my function. Can please someone hlep mi fix this code:

function vr = simpson2d(f,a,b,c,d,n,m)  
x = a:n:b;
y = c:m:d;
h=(b-a)/n;
vr= h/3*(f(xi(1))+2*sum(f(xi(3:2:end-2)))+4*sum(f(xi(2:2:end)))+f(xi(end)));