NATS ant-theft system

I replaced an air filter on my car before starting the engine.and then i went to start the car nothing happened. A car symbol with key started to flash. Nats anti-theft is enabled. I tried everything the manual states to deactive it but did not work, every time I turned key the central locking keeps locking and unlocking. I have now nearly drained the battery. Don't know what to do. Is it worth ringing the RAC as I am a member, would they know how to deactivate the anti-theft or could I remove a fuse.. Thankyou Nick
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