I had the exact same problem, buying a miner from Innosilicon. In my case it was the T3+. I tried everything, inclusing firmware update, flashing the firmware via TF card, you name it.
The solution was easy, provided by the customer support of Innosilicon, after constantly bugging them for over 5 days: they emailed me an UNLOCK firmware.
The download link is in the description of the video: https://youtu.be/vaj_gymDUHQ