Filtered signal does not follow my cut off frequency
did i make some mistake ?


Yes. The cutoff frequency is specified relative to the Nyquist Frequency and not the sample rate

From the documentation


  Wn must be 0.0 &lt; Wn &lt; 1.0, with 1.0 corresponding to half the sample
  rate.


Also: you design a 10th order butterworth and filtfilt() doubles that again to 20. That will give you significant domain "ringing".