Hi Duibhcek, it sounds like you're doing all the right things already.
let the wd40 time to soak in,

perhaps try rotating the pin using a pair of vicegrips, gently though! small movements at first building up- then knock out with punch

worse case, remove the caliper, rest it on a solid surface- a vice would be good! now try the pin punch. a solid resting surface allows all the energy of the punch/hammer to be delivered where it can be more effective

when out a good clean with sand paper and a liberal coating with copper grease should see you sorted!

That Welsh soil certainly tested a few bikes! my problem is at the manufacture being checked to see why it failed, should know today if it's repairable.