chimney leak neighbours roof

Good day everyone, Before the neighbours had their roof done in 2021, there was damp in this corner. Since then, I thought the issue was fixed—the area was decorated but still looked stained—so I didn't think it was a fresh leak. I had my roof done by some cowboys last year, and I thought...

My neighbours have built a dormer 18 months ago, we have a shared chimney stack, they have said that my side of the chimney needs repairing (which I agree with after seeing the photo) and this is causing a leak in their bedroom which is under the dormer but the leak is in the recess to the side...