or these:
Ditto that !
These things also seem to work miracles !
Or, you may want to go the "Old World Way"
One suggestion, if everything you've tried won't work.
The oil drain plug on my bike is 14mm.
Never mind how much that is in inches, it's 14mm, period.
Get a file and file away a little where you can reach in order to have one flattened side, and file away on the opposite side, so you end up with a... flattened round head.
If you file away enough, you can slip a 12mm or a 1/2" wrench and give it a twist.
Last - see if you can find a Torz nut with the same pitch as the 14mm nut.
Nuts and bolts will get rounded out, Torx? Never !