Update for those who care.
Took it in to the shop today and they were quite apologetic (not very but not sure what I expected tbh) and took it in straightaway to give it a once over. I went away for an hour and when I got back they seemed to have done it and as a bonus fixed the puncture I had got in the meantime as well as fitting a new Middle ring that I bought thinking it probably should have been replaced during the service.
No mention of a discount in the future or any other perk (other than a free tube I guess) but at least the bike is working. At least I hope so, not actually ridden it yet.
I shouldn’t think I’ll use them again if I’m honest, just because…
Also, and this might be a common thing with bike services…but do you normally get given the old stuff they take off to replace? You do with car services. And I didn’t with this bike service. Recognise this makes me sound a bit tight, but tbh I would have recycled the old chain on a pub bike…