I restore 70's and 80's motorcycles so I often run into frozen fasteners. Here are some things to try (usually in this order):

Allow PB Blaster to soak and tap with a hammer

Apply heat

Use an easy out (with reverse drill bits)

Weld a washer on to fastener (or what's left of it) and weld a nut on to washer giving u extra leverage

Sometimes it helps to alternate between loosening and tightening directions. I've had some incredibly tight bolts that first moved in the tightening direction, then came out.