After determining to assess assessable costs against a responsible party, the City Treasurer shall mail an itemized invoice to the responsible party at its last known address. The invoice shall be due and payable within 30 days of the date of mailing and any amounts unpaid after the date shall bear a late payment fee equal to 1% per month or fraction thereof that the amount due and any previously imposed late payment fee remains unpaid. If a responsible party shall appeal assessable costs determination of the Mayor, the costs, if upheld, in whole or in part, shall be due and payable 30 days from the date of determination of the appeal of the decision of the Mayor to the City Council and any late payment fees shall apply thereafter.