It's simple, knowledge is the answer.
Go to the public library or find a british person to find out about what kind of curses and magic are being used and how to stop it. If any magical situation happened in real life there'd be legends about it, and usually all immortal things have a weakness.
Vampires are dead, but you can kill them with a steak through the heart.
Demons are dead but Constantine kills them (lol)
Crazy warlock/necromancer probably has some weakness.
Everythings got a weakness, i bet stabbing michael myers with the femur of his mom would probably kill him