imei problem

A

AC Question

i have been using note 3 n-900 from the past one year and i am very happy with the features if that phone. I usually update my phone whenever there is a OTA update. These days i am experiencing a problem with my imei number. My imei number is getting changed unnecessarily. I have not updated my firmware through any unofficial sources. Moreover i don't even use any third party applications/accessories. I really wonder why my imei is getting changed without doing anything. Is it because of updating the firmware through samsung Kies or is it because of any other reason. Please help me know what is causing that problem.