Well had a look today and fixed the seatbelt myself (although managed to crack the plastic cover in the process thanks to being about as gentle as an elephant lol). The sliding seatbelt height adjuster hadn't been clipped over the actual adjustment catch and nut, and was fouling the seatbelt enough to stop it retracting.
And appreciate the tech comments re wiring locations. Whilst I don't believe I was being lied to (they clearly did strip back the door pillar, albeit unnecessarily, and SO FAR the fix they claimed to have done in the roof wiring has worked), their failure to fix the fault correctly in the first place, and subsequent inability to reassemble the door pillar correctly, has got me looking elsewhere for a garage now sadly
