Hammer the biggest Torx impact bit you can in, then a ratchet and socket on the end of that. works every time.
Good bit of advice by the blackwidows, if a larger torx bit will not fit then enlarge the hole very slightly by drilling out then hammering in the torx bit, the hammering or “direct applied percussion” in engineering terms will most likely shock the initial seized head/thread and it will come loose. By use of torx bit i mean an actual hex drive torx bit not those crap angled soft cheese L-shaped things you get free with brake rotors, they’re only fit for the bin. When you fit new cleats slather the bolts in coppaslip or another such antisieze compound.
theotherjonv : Be careful as you will eventually stretch the bolt threads to such an extent that they will become loose in the cleat plate as fitted in the shoe, coppaslip or another antisieze compound will do a better job and torque the bolts to 5-6 Nm or 3.5 to 4.5 lb-ft (shimano specs).