The only time I've had to do this I used a hammer and chisel....forced the chisel behind a thick stem...loosened it and pulled like billyoh! Lots of times but it was so satisfying when a very long and high stem came away.
Crafty...the incident with the flame thrower was a temporary lack of concentration when the builder turned up in shorts.
Anyway....the police are returning it soon...:-(
Don't know if it's on a tree or wall, in either case cut out a section of the stem near the base and remove a section of stem about 4 inches long, if you only make one saw cut, it can grow back together.
When you later see the leaves starting to wither and fall, that's the time to start pulling up from the bottom.
Old cloths old tools plus eye protection and dust mask, highly recommended!