Was this a PAYG line, or a pay-monthly?
You've posted in the "pay-monthly" section, but the only reason for this to be cancelled would be by the account holder explicitly giving 30ays cancellation notice, or by using a PAC/STAC to transfer your number.
It's quite common for low-usage PAYG users, to fall foul of the hibernation process if they don't use their phone at least once every 6months.
