Just an update: I received a reply from Scotrail this afternoon (presumably re: plusbus):
Never mind 7 days, it's almost been seven weeks! I know we've had a lot of bank holidays, but come on! I'll let you know what they say about the whole thing if and when they get back to me (probably by Christmas at this rate...)
Thank you for contacting ScotRail. Under the terms of our Passengers' Charter, we aim to respond to all claims/correspondence within 7 working days.
Never mind 7 days, it's almost been seven weeks! I know we've had a lot of bank holidays, but come on! I'll let you know what they say about the whole thing if and when they get back to me (probably by Christmas at this rate...)