EdrZero

Yes, after almost a year I decided to look again and finally find the answer.
This time I tried with UART4, change the pins and everything as I posted, and then, only one more step was needed to make it work.
 
first, you have to read the file /boot/dtb/overlay/README.sun7i-a20-overlays
in there you will find all the information about the overlays. 
 
then go to /boot/armbianEvn.txt and put this at the end of the file:
 
overlays=uart4
param_uart4_pins=a
 
then restart and Bingo!! UART4 now works like a charm!!!
 
Hope this helps.