As a contractor you are responsible for paying you own ACC levies.
You will be invoiced by ACC for a Worker Levy and Working Safe Levy at the beginning of each financial year. The levies are calculated on your earnings for the previous 12 months.
You will not receive an invoice for the first financial year in which you are a contractor, as there is no previous year's income to calculate the levy against.
ACC will send you an invoice at the beginning of each financial year that you are required to pay ACC levies.
You can find more detailed information here on the ACC website.