About ten days ago I had to cancel a (fully flex) booking ... first time I've ever done had to do this. It still hasn't gone through yet, I phoned again in a couple of days ago and was told there was a bit of a backlog at the moment. I think this may be due to a recent meteorological event affecting parts of the US, so I can imagine there is a bit more activity than normal in this area... but how long should this take?

I can see remnants of the reservation in MMB - the PNR is shown but with a completely differently date & flight to the original one (date is now at the end of this month). Looks like some kind of stub record: