I think that when my mate had his chimney done, they dropped a stainless flue down from the roof.
The hardest part was getting the scaffold to the chimney.
I've had the misfortune to have installed many hundreds of flue liners . Mostly gas but a fair few twin wall when asked how long will it take? the reply is between 3 minutes and 3 days I've had both!.
If your liner really is stuck fast it's a chop hole in stack and free it probably stuck on a gather over.
The awkward ones are definitely a 2 man job one on roof twisting and pushing one at bottom on a rope gently pulling.
Can be a truly awful job I wish you luck.
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