I've been known to use a cutting torch (poorest choice), a Sawzall or a nut splitter. Unfortunately that bolt is probably too rusty to reuse so whichever way you go, you still need to find a way to use a new fastener. The ancient scars on my arms attest to many hidden and rust frozen fasteners on motor vehicles.
Dave W along with my DW, Susan and our poodlepups, Callie & Molly,2011
Ford F250 6.7 CCLB, 5er Hitch Option w/B&W Hitch,,Ride Rite air bags, 2014
Montana High Country 343RL (38')