One thing what I saw was that when I had a payment method it didn't reach to the enroll page and would fail at first step saying request could not be completed. I contacted the support and they mentioned the same that my account could not be enrolled and they don't know the reason, Asked me to create a different apple account and enroll. Even that didn't work then I tried to remove the payment option and then gave it a try it worked and at the end I got the same error as you do. "There may be an issue with your account that needs to be resolved before you can continue. Please contact support." I don't know what to do, Even with a different apple account it didn't work, tried doing it from Mac and iPhone. Failed in both the places. Any luck here?