Remove the 50 Hz Hum from a Signal

I have a signal which contains 40Hz and 50Hz values and it's FFT is like:

how can I remove 50Hz signal from it?

I tried second order filter but it getting worse: here is the filter code :

d = designfilt('bandstopiir','FilterOrder',2, ...
               'HalfPowerFrequency1',49,'HalfPowerFrequency2',51, ...
               'DesignMethod','butter','SampleRate',Fs);
           

and then: where u is the input signal,

 filtering = filtfilt(d,u);
 

the result is:

does anyone know where is the problem?

U which contains 40 and 50Hz signals is :

Answer 1

[Star Strider]

The designfilt call designs a second-order Butterworth filter. It appears to be correct when I analyse it with freqz. Without seeing your data, it is not possible to determine what the problem is.

An alternative filter design is:

Fs = 900;                                                           % Sampling Frequency
Fn = Fs/2;                                                          % Nyquist Frequency
Wp = [48 52]/Fn;                                                    % Stopband Frequency (Normalised)
Ws = [0.9 1.1].*Wp;                                                 % Passband Frequency (Normalised)
Rp =  1;                                                            % Passband Ripple
Rs = 90;                                                            % Passband Ripple (Attenuation)
[n,Wp] = ellipord(Wp,Ws,Rp,Rs);                                     % Elliptic Order Calculation
[z,p,k] = ellip(n,Rp,Rs,Wp,'stop');                                 % Elliptic Filter Design: Zero-Pole-Gain 
[sos,g] = zp2sos(z,p,k);                                            % Second-Order Section For Stability

figure
freqz(sos, 2^18, Fs)                                                % Filter Bode Plot
set(subplot(2,1,1), 'XLim',[0 Fs/5])                                % Optional
set(subplot(2,1,2), 'XLim',[0 Fs/5])                                % Optional

filtering = filtfilt(sos, g, u);                                    % Filter Signal

Provide the correct sampling frequency (I assume it is 900 Hz from the fft plot).