I was under the impression unused credit disappeared at the end of the month

It doesn't appear to, our neighbours used it a month after Red bought it and had no issues, I thought it was because it was PAYG.

It didn't used to expire; but now it's 30 days from activation... or at least KW's is.

Hmm, maybe not then, Red bought ours on the 27th June and our neighbours used it last week so perhaps it has lost its remaining credit now since it's just the month end now *hmmm* Well, if you want to put some credit on it Foggy to try it out before you sign up to a contract you're still welcome to.