Accuracy value constant even after different runs
I see that you have set a Random Number Generator(rng) seed in the following line in your code: rng(1).

So, this splits the data in the same way no matter whichever run. So, that is the reason why you are getting the same error values.

Try removing the line. Then, the data shall be slit randomly (as there is no seed now). You shall get different error then, depending on how the split is done (which is, randomly).

A model which generalizes well should be robust to the choice of seed