How to smooth filter response?
You have a very narrow stop band which means that all the poles are crammed in a very small area of the complex plane, close to the unit circle. This can result in severe numerical problems, even for relatively small filter orders, even with floating point arithmetic.

Another important point that you might not realize is that if you design a band pass or a band stop filter using the command cheby2 (and all other similar commands), then N is the order of the prototype low pass filter, and not the order of the resulting band pass or band stop filter. So if you choose N=14 then you've designed a band stop filter of order $28$. Such a filter is very hard, if not impossible to realize because of numerical problems.

Also note that calling cheby2 with [z,p,g] (zeros, poles, and gain) as output argument usually results in higher accuracy than using the polynomial coefficients.

I would actually suggest trying a notch filter instead of such a narrow band band stop filter.