fttsen,
What version of Android is your Lenovo P780 running?
The Fenix 2 uses bluetooth low energy, not bluetooth classic to communicate with Garmin Connect Mobile (GCM). Android doesn't support BLE until Android version 4.3. According to the http://shop.lenovo.com/ae/en/smartphones/p-series/p780/#tab-tech_specs, the stock Android build on that phone is verson 4.2.
Please update your Fenix 2 to version 4.40, using Garmin Express http://software.garmin.com/en-US/express.html and answer the above question, and we'll go from there.
Thanks!