Awful service -- correct complaint procedure

What is the correct procedure raising complaints to cover ourselves

We have contacted our solar installer about various things and the responses have not been "great".

Today we noticed a hole in the roof (missing tile) right next to the panels and also a good few cracked ones (again right next to the panels). (Roof is very high so only viewable from a distance -- spotted what I thought was a mark -- used binoculars and it is a missing tile -- scanning across spotted the cracked ones.

We are going to email the photos I took with polite request to fix -- I have been a member of test achats for a few years -- not used their services yet (suspect this will be the first!)

Does an email count as contact -- or should we send registered post -- ie in the email advise we are also sending via registered post (email so they get the info quickly)

Do I have to leave a hole in the roof to give them opportunity to fix? - what is reasonable timescale to allow? We do have winter weather coming!

Thanks