Did you renew your contract before or after you moved to London? I know you say you moved in January and halfway through your contract?
If you are on Refresh you could pay off the device and give 30 days notice for the airtime. You need to work out the cost and whether you can continue to manage with no signal for the rest of your contract.
Obviously you could make a complaint and go down the route of trying to leave without penalty, others have been successful in doing that.
No need to post the link as you are ex-staff so you really know all this.
Track usage, upgrade and get support with the My O2 appDownload My O2