I think that you just need to do:
Fs = 500;
fcutlow = 6;
fcuthigh = 14;
[b,a] = butter(6,[fcutlow,fcuthigh]/(Fs/2));
Filt_filt_signal = filtfilt(b,a, rawSignal );
without "Butterworth_bandpass_filter = filter(b,a,x);", otherwise you firstly compute a filter on the signal (with phase lag), and then you pass the filtered signal into filtfilt routine that filter again twice the incoming signal, but the incoming signal is already with a phase delay.
If you wanto to be sure about the results, have a look the frequency domain, comparin initial and final spectrums.