Thank you both.
I can tell you now, that I was not banned. Not even my IP address was banned by the forum.
I got an e-mail from the board admins as reaction to the mail I had - after some struggling with the forum software which did not want me allow to do this(!) - send to them. They told me, that there was never a ban against me or the used IP address. It was a problem with the forum software respectively its setting - or in my words: The software went crazy. This should also be solved for other user who got "banned".
What really made me nervous was the point I reached on this noon, when I was not able to log in and I was at first also not allowed to send a mail to the admins. With some persistence I finally got the mail to get submitted. But imaging I would not have been able to do this, nobody would have been able to tell, why I am suddenly absent, if I died, if I moved away (no I do not have such tendency) or if something else has happened. There was at first even a point, where I was not even allowed to read the forum logged off (only the banned site was showing) and to search for the e-mail address to contact the admins via Thunderbird. I hope, that I will never get again into such a situation.