Let's face it, ACPO is selling access to data for profit. It is data that is collected at public expense, and then sold for gain by ACPO, which is a private limited company and itself beyond the reach of FOI legislation, just as is the RSPCA. Just as the RSPCA dress up and masquerade as state officials in their uniforms, so does the chairman of ACPO, a retired copper who parades in a uniform giving the impression that he is a serving police officer.
You will have to write to individual chief constables, or P&CC's. They have some public accountability, but there is no P&CC above ACPO. Hence no public accountability by ACPO.