Hi  I've done last update firmware 03.500 and after this the rc will not connect to my iPhone. But it still connected to mavic. I've tried to reinstall DJI go  and it didn't work also tried to downgrade no luck.  But I noticed that RC would not connect to the PC. When I plug it in to PC the RC begins changing and PC saying it couldn't recognise it. Also tried connect the iPhone via wifi to the drone and it works perfectly.  Need help pls.  

The cable your using is good isn't it and which port on the controller are you using? If your using the full sized USB in the bottom it won't work unless the cable on the left hand side is disconnected.

If your using the left hand side cable try using a USB cable in the bottom see if that works

Also do you have another device you could possibly try?

Could you please clarify what mobile device you are using?
Please try ah93's advice and keep us posted.