Assuming that you downloaded “/usr/share/X11/xorg.conf.d/99-calibration.conf” as described in step 8 in post #5 try changing the content of this file to:
Section "InputClass"
Identifier "calibration"
MatchProduct "ADS7846 Touchscreen"
Option "Calibration" "227 3936 3880 268"
Option "SwapAxes" "1"
EndSection