I have the same phone and the same exact thing has happened to me. Its terrible that the only way to fix this is to get a new phone and customer service doesnt even understand that so they just send you to LG.
The No Service problem is usually caused by a bad IMEI number. Please go to Settings> About Phone> Status> IMEI. If it says 'null or unknown', then LG needs to restore the IMEI configuration. Please let us know.