I've been banned off of Line for the crime of doing literally nothing. I created an account before a trip to Japan so I could add Japanese people I already knew or might meet while there.
I made the account without any significant issues, got the QR code to add a friend then got an unspecified error any time I tried to add them. I tried adding an official account with the same error. I looked it up and saw some suggestions about waiting a few days to try again so I did just that with the same results for any official account or my friends account. My brother made an account and tried to add our friend with the same results, then found that when using my QR code it said the account didn't exist.
After digging more into it and trying to figure out what was up with Line's support directly all I could find was an FAQ that said if you got an unspecified error when adding someone then it means your account violated Terms of Service for sending illegal messages, harassing people, etc that type of stuff. Still have yet to figure out how exactly either of us did any of those things before we could send a single message, but I'm sure it's a very good and logical reason which would surely also explain why Line doesn't answer my tickets or emails. Surely.