LG C2600
Invalid imei numbe

I purchased a LG mobile phone model number C 2600 from an authorized LG mobile showroom I received a message from my service provider (IDEA) that my phone has an invalid IMEI number. I haven't changed my phone software or neither I haven't done any phone service after buying this phone. The service provider's says that I can't use this phone further because this phone does not contain a valid IMEI number.