This is indeed a misunderstanding, the word ''dik'' or ''fat'' in general should not be mute or warnable unless you say the word ''dik'' (referring to the male private part) to bypass the word filter.
Contact the staff member who banned you like
@ElPtricko said.
If you said the word ''dik'' in or with any sentence, translate the sentence too to prove that you were reffing to the word fat and not to the English word (using the screenshot where you got warned for). Your warning should hopefully be taken away after this.
If you have any other prove that you were referring to the dutch word, definitely mention/give this.
I hope this helped.