Unable to filter noise and powerline interference from head and chest ECG before averaging

I have recorded 2 signals(1.chest ecg 2.head signals). The idea is to detect the R-peaks of the chest ecg and to get the averages of head ecg and chest ecg from the respective head & chest recordings. However, the problem that I always face is these recordings are always corrupted by noise and powerline interference (based on my FFT(figure 2 & figure 3);correct me if I am wrong).

In order to get very good averages, I have to first filter these signals with appropriate low-pass filter and notch filter. My iir low pass(100hz) and iir notch(50hz) doesn't seem to work as expected.

As you can see from my current code, there are lots of spikes on my averages (figure 5 & figure 6).

Please recommend me the the right filter that I should apply to these raw head and chest ecg signals before I perform the averaging. I will really appreciate a code example tested with my data(krest.csv).

Attached are the: 1) Feb1_18.m %The main file 2) ensemble_avg.m %the code to perform the averaging operation 3) magspectrum.m %to calculate the FFT of the signals 4) Rwave_modified %to detect the R-peak location 5) krest.zip %my data after unzipping(krest.csv)