The enforcement authority shall cause to be issued an invoice for the service charges accrued. Such bill shall be due and payable within fifteen (15) days after the billing date. Failure to pay after sixty (60) days from the billing date shall result in an additional ten percent late charge per each response invoice. Unpaid bills may be referred to a collection process after ninety (90) days delinquency or be assessed against the parcel of land pursuant to Section 38773.5 of the Government Code as amended and shall thereafter be transmitted to the tax collector for collection. (Prior code § 4505)