Proceed to do a phone number transfer (requested a month earlier) to voip the day before all your staff go on holiday, without telling your customer (so when the phone suddenly stops working they have to ring you to find out why).
Then screw the transfer up, so your customer's phone number no longer works (no routing) until the 7th of January because anyone who can do anything is on holiday.
That would be the entire Christmas period, where people actually want to call each other.
Well done.