Let me guess, the plug was hand tight? The tech clearly wound it in by hand to stop him losing it, then forgot to tighten it up. Human error it happens, it's frustrating but no-one's perfect.
The tech does not want to own up so tells his boss he did tighten it, boss has no choice but to accept his word and so then comes back to you. If it were me, I would CALL HIM (no email), put on a nice smiley voice and just suggest that's what happened. Tell him you're not that bothered, that mistakes do happen but no serious damage was done, and suggest to him that he purchases and fits the gaitor for you and you'll call it a good job and will be back in the future.
If you go postal at this point he won't offer you any more, so I'd play super nice just to get the result I wanted. People respond better to compliments and pleasantness than when customers get stroppy.
Stroppy can work, but I use it as a last resort.