Anr I was going to recommend a cutting torch

Can you get at the 3 screws holding the filler flange on? Remove it with the cap still attached and depress the ears from inside once it's off. Tried some WD40 around the seal area and pushing in while you turn the key? Might be worth calling Keyhole locksmiths and seeing what they say or can do, they make housecalls AFAIK.