That was a year and a half ago.
It's not the time that counts, it is the offence that does. Whether you did it yesterday or before 2 years, you are guilty of it and you deserve to get the punishment assigned for the offence in the present.
I am 28 years old and I am already an adult
A 28 years old adult who doesn't even have the sense to understand that a place cannot be without rules, and offending them would get you ended up with a punishment. A person living in a country needs to know the laws in there and obey them, same goes with a forum.
I don’t want to shed tears here, but I’m very sad that because of my stupidity, now I can’t communicate in my favorite forum.
Shedding tears won't help you. You call it your favorite forum, but as far as I know, people never get careless about the things they posses which are their favorite. If they do, they lose them, and that is what happened with you.
I made a mistake once and ask moderators and administrators to change their decision and give me a temporary ban.
It is not once, the reports above show that you have done it more than once, and something done more than once cannot be a mistake.
Even for a murder they do not always give a life sentence.
They do, if they manage to catch the murderer.
