Hi,
Just for the record I had exactly the same thing on the first oil change in my ownership, and solved it almost exactly the same way. Posted a few months-ish ago. Plug would not release. I didn't fancy it, but non the less in the end approached the warm engine armed with an 1/2 socket and a (too) long bar,

used 2/3rd of its length in a controlled manner and it cracked off.

Engine had witness of a blue tinted sealing-retaining fluid having been used on the plug at some time previous. I hope that retaining fluid was the major part of the problem, rather than over-tightness alone. I then refitted with a torque wrench at the correct value, and filled with Morris 15W40.
Gotta say it very important to high-light a few things here:
A breaker bar can do mucho-damageo. Steel plug plus magnesium crank case x lots of force can = a world of pain.
I almost didn't post this as this course of action, it is to me a very last resort, and a bit too far 'off-piste' to be considered a reach-for, recommend solution.
That said this does represent another case for the record. It was the second oil change for me when I finally released my sump plug:- gave up the first time and used the bolt in the plate described in previous posts.
Whist not having done loads of road vehicle repair work, I do have 30 plus years in engineering w-shops behind me, so have a degree of mechanical sympathy, and feel. If anybody does do this then as soon as one gets the slightest inking that it isn't going as intended then STOP and reconsider other solutions in the forum, like heat /cold etc.
2.0l C.U. Air-cooled 1983 Autohomes Kamper