Ok, then you need the overlay… 
Did you already try the settings recommended by Waveshare for “99-calibration.conf”? If not substitute the content of “99-calibration.conf” with:
Section "InputClass"
Identifier "calibration"
MatchProduct "ADS7846 Touchscreen"
Option "Calibration" "73 4007 3976 84"
Option "SwapAxes" "1"
EndSection
These values have been taken from here. You may also try the differing values from the wiki page your link is pointing to.