Vercat Issue with 3D plot

I am generating a code for two cylinders, and even though I manage to plot them on 3d as desired by the use of hold on's, when attempting to generate a large matrix summarising both cylinders, I get a surface connecting the two shapes that I have not defined anywhere. My code is:

[x,y,z] = cylinder(50,500);

mesh(x,y,z)

hold on

[x1,y1,z1] = cylinder(45,500);

z1 = z1* 10;

mesh(x1,y1,z1);

hold on

[x2,y2,z2] = cylinder([45 50],500);

z2(1,:) = 10;

z2(2,:) = 10;

mesh(x2,y2,z2);

hold on

[x3,y3,z3] = cylinder([45 50],500);

z3(1,:) = 0;

z3(2,:) = 0;

mesh(x3,y3,z3);

hold on

[x4,y4,z4] = cylinder(20,500);

z4 =  z4*10;

mesh(x4,y4,z4);

hold on

[x5,y5,z5] = cylinder(25,500);

z5 =  z5*10;

mesh(x5,y5,z5);

hold on

[x6,y6,z6] = cylinder([20 25],500);

z6(1,:) = 0;

z6(2,:) = 0;

mesh(x6,y6,z6);

hold on

[x7,y7,z7] = cylinder([20 25],500);

z7(1,:) = 10;

z7(2,:) = 10;

mesh(x7,y7,z7);

hold on

x = vertcat(x1,x2,x3,x4,x5,x6,x7);

y = vertcat(y1,y2,y3,y4,y5,y6,y7);

z = vertcat(z1,z2,z3,z4,z5,z6,z7);

mesh(x,y,z)

I want to get rid of the surface which matches the two cylinders. You will be able to see the shape I want if you delete the last three lines of the code.