Had it happen a few times.
This has worked for us.
If you get a jubilee clip slightly larger than pole diameter, slide up the pole to where it meets and is stuck.
Tighten, but only till snug on pole and so there can be movement.
Hit the clip where the adjustment screw is, forcing one pole end away from the other, and move the clip around opposite to where its positioned on pole to keep it even all round.
A good few strikes has always done the trick over twisting, heat guns, hot water.
Might get a little cosmetic damage but very little, and you can always put a bit of tape round first, although I have never bothered.
Handy for someone to hold the other end as well.
Good luck