That's pretty harsh treatment, but not rare by all accounts.
It sounds to me like they already knew that 'Carl' was possibly joining their band, but were hedging their bets.
Not a great deal you can do - either ignore their message, give them a load of abuse, or try to do the diplomatic thing & stay 'friends' (!)
I think if it were me, I'd go for the second option of kicking off, but then that might not be wise...
Good luck with everything, and remember, you did everything they asked - they failed you.