Open Payables Report

There are invoices/credits on the report that should be removed. Example: An invoice was entered and then a credit for the same amount was entered. The net result is zero. However the two line are still showing on the report. I tried to remove the lines by AP35. However, it shows no invoices for that vendor. The invoices are prior period/year. Does that matter? Or, could I remove the two lines by AP55--even though it is prior period?
Thanks for your help. I have asked several people in our company and not even the corporate acct seems to know.