My guess is that it was left with the handbrake on and either the cables or the shoes – or both – have seized.
Heating the drums is unlikely to free seized shoes or cylinders.
Suggest you start by wiggling the cables to free them if sticking. If they are steel covered an application of WD40 or similar may help.
This is unlikely to release stuck shoes but, with the hub nut released, gently tap around the outer back edge of the drum – preferably with a soft (leather or nylon) mallet to drive the drum off. Avoid heavy blows with a steel hammer which could fracture the drum.
B….
Bernie