I am having issues linking Phantom 4 v2.0 drone to controller (Android DJI GO 4 app)

I am using the following 2 ways to link with no success:

• Pressing C1 & C2 & record button simultaneously until blue flashing light then pressing link button on drone - will connect for split-second then disconnects and requires me to start process all over again
• Within DJI GO 4 app going to Enter Camera View then top right 3 buttons - Remote controller seetings - then selecting Remote Controller Linking - no success
  

Anyone with similar issues and can recommend what else I  can try

I have ensures latest Firmware update
I have tried Factory Reset

Hi there, thank you for reaching out. Please try to refresh the firmware to see if it helps.

Also, please ensure the connecting steps are correct.
Force start linking by pressing the C1, C2, and recording buttons simultaneously. When you hear a sound from remote controller, press the gimbal dial on the right for 2 seconds. Find the linking button above gimbal, press it for 3-5 seconds, and wait for the LED indicator of remote controller turns green.

If the issue still persists after trying, please send back for comprehensive check to ensure the long-term usage. You could register through the following link, https://repair.dji.com/, to create a case and send back for further processing.