Thank you both for your help. I do have videos but they're too long to be posted here. I'm going to try the "Local" section on this site to find someone to do the repairs. Or if anyone in the PE13 area reading, please get in touch. Thank you.
I am at the end of my tether with the installers. My extension was completed October 2022 and immediately I've had leaking guttering with water seeping down the walls. They've tried many "fixes" but mainly with a sealant gun.