So the company did not send an engineer as booked, presumaably because I suggested I wouldn't pay their £75 call-out fee if the problem originated with their initial work.
Freesat was working again... till this evening. Now again showing 'no signal'.
I've found the 'signal strength' (100%) and 'signal quality' (100%), but despit this 'no signal'.
LNB power shows green (on) and DISEqC (whatever that is!) is off. Unicable (?) is off. If I turn it on, signal strength and quality go to 0%