You were banned for using a word that is a common representative for the f-bomb. This word is treated just the same as if you were to say the real expletive and this is a violation of the chat guidelines, and i have highlighted the violation below;
5. Offensive chatting
Messages of an offensive nature are not allowed.
This includes, but is not limited to:
-Using vulgar, profane, or sexually explicit language or abbreviations of such
-Using race, religion, sexual orientation, culture, ethnicity, handicap, nationality, or gender as a means of insult
-Using sexual preference terms as a term of insult in any way, shape, or form
-Using threatening, harassing, defamatory, hate-speech, or libelous language
-Providing or requesting links to or material from pornographic, obscene, or hate-speech web sites
-Providing links to web sites with potentially offensive content without a clear warning
-Descriptions or details about any sexual act or sexual organs
-Using three or four letter acronyms that represent bad language will attract a ban just as if you had said the words.
-Using *,#,@ or any other combination of numbers or symbols in a word to disguise it or push it past the filter will represent bad language and will attract a ban just as if you had said the words.
Therefore the ban will remain in place. Should you have any further questions regarding this ban, please feel free to contact support.