Tim Campion already pointed out the FAQ post: What can I do to lift or reduce a suspension? I will add also link to another answer on Meta Stack Exchange: Where I can complain about an unfair account suspension?
Apart from replying to the moderator message, you can also use the contact form to contact Stack Exchange Team. On MathOverflow you have also an ...
As far as I understand, there is no rule against opening a meta post to discuss your own ban and defending yourself; especially if you wish to draw the attention of the community to a ban that you find unjust.
Here again is the relevant meta SE question on appealing suspensions.
Here is some general advice for users who have been suspended.
It's natural, when being disciplined, to feel defensive, or to feel wronged.
But remember that one purpose of the suspension is to give you time to reflect on your behavior, and to try to understand how you can change your ...