This gets better...

I've just picked up a voicemail from Friday to say 'yes, we got it wrong, we were overcharging you by £80, tax amount is now £482', (as per the LOT site)

I then go in to check the reservation to find (drum roll...) that the BRU-ORD-LAS flights have been cancelled.

Reason: BMI failed to ticket in time

Cue call to the ICC who were as useful as a chocolate teapot...

The cancelled flight hasn't been released back into reward inventory.

"Sir, if you can't be flexible on date then there's nothing we can do to help you"

They were seemingly unable to comprehend why I had an issue that their f-up in not ticketing quickly becoming my problem was in some way bad.