I have the same problem. When I clicked on Change Character, only my Battle Tag is displayed but no characters.
On my phone I logged out and then logged in to try to fix the issue and I lost access to all characters. I can no longer post using my phone, it says that I need a level 10 character. And I have lots of 10+ characters.
I opened a ticked and started a topic on the technical support forum. Feel free to write about your issue in the same topic:
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