They were given three months in advance but only via the bnet launcher or external WoW specific news sites. No email was sent to account holders informing them that this was happening, unlike the emails sent to account holders informing them that the cloning service was live.
What’s done is done, but “You were informed” isn’t a valid response to anybody who didn’t have an active subscription at the time the cloning service was shut down. There was no reason to expect this to be a limited time service and it would appear that a large number of players were left unaware that they needed to act.