You are doing everything correctly, however you only need to use the second-order-section (‘sos’) representation, since it essentially guarantees an efficient, stable filter. Transfer-function implementations can produce unstable or unreliable results.
What may be confusing the issue however are the arguments to the ellip function. This designs a second-order filter with a passband attenuation of 20 dB and a stopband attenuation of 25 dB. It may be worth reconsidering those values in order to get a usable filter. I suggest that you start with the ellipord function, and go from there.
[z,p,k] = ellip(2,20,25,200/210,'high');