Remove AC component from the mixed signal using an elliptic filter
I agree, the 1 Hz signal should be attenuated given the filter response. I suggest sweeping the input frequency to create the frequency response manually as I assume the filter was somehow scaled, possibly by not including a factor of $T$ in the mapping from the analog filter. Try a much higher frequency to see where it is nulled and then narrow in on the actual cut-off.

Further notice that the frequency response is not completely nulled at 1 Hz, but would have about 65 dB attenuation and that it also contributes significant phase distortion to the passband.

Instead of using an elliptic lowpass filter, consider using a 2nd order notch filter for eliminating AC signals. This implementation is detailed further at this post:

Transfer function of second order notch filter