Same here. They took their sweet time sending out the final bill and when it came it didn't have a cheque in it. Imagine my surprise... not.
They say they send the cheque out 30 days after disconnection and that it can take 15 days (count 'em) for it to arrive. I'm coming up to 45 days since my disconnection at which time I fully expect to have to call them to threaten them so that I can get my cheque.
It's just another technique to try to hold on to your money. Don't let them win.