This depends in large part to the type of account you have, and what date was set for cancellation.
For all accounts, as long as you contact us before the account is closed, we generally can revert the status to active. However, note that the billing department (which handles these requests) is only open during business hours on weekdays, so be sure to contact us at least one business day before the account is set to close.
In some circumstances, a deleted account can still be restored, but that will depend on your service. For instance, most dedicated servers are held for at least a few days after cancellation (although we do not guarantee it), while most of our shared hosting accounts are automatically purged as soon as the account is closed.
Again, while we cannot guarantee that we can bring back an account that is already closed, we will certainly be happy to if we can.