Hello @lb_232598 and sorry to hear that. I am assuming you get no errors from the procedure you linked?
The suggestion to double-tap RESET will not work in your case as I suspect your Flash is fully erased, so no "Arduino bootloader" is present to handle the double clicks.
I just had an idea for you to test. Can you repeat the bootloader recovery steps on your board with also B0 shorted to GND? It's on the same side as the usual B1 but closer to the USB connector.
What I mean is this:
- short B0 to GND with a jumper wire so that it stays that way the whole time
- do the normal ROM boot mode procedure (short B1 with GND, press and release RESET button, remove short on B1)
- proceed with the recovery procedure as usual
- remove the short on B0 in step 11, after the flash is complete
During this test the LED will light on different colors - don't worry, it's harmless. 
Let us know if that helps!