Thanks for posting, sorry to hear of this billing dispute.
I can confirm that any refunds due, are sent within 35 days of the disconnection date. If the account is now cancelled, then a few days after the disconnection date, a final bill is generated. This bill is usually a credit, which covers the period of no service, as we bill in advance.
We send the returns packaging the day after the disconnection, and it can take upto 14 days to receive this.