it did have a rubber seal on it, and the washer i ordered was metal (intended for mx-5), okay i guess it was some garage’s work to use the Mazda 2’s sump plug 
. I also have the new sump plug on to which the 17mm socket fits perfectly.
Use a Metal Work Chisel to rotate the screw. Looking at the Pic, to the left.
Looks like two of the flats are vertical. I’d just take my time with a square edged file on the flats until there’s a tight fit with an open spanner.
Then a bit of heat for good measure and it should simply undo.