Have you spoken to your MP? If not, do so. Try to meet face to face with her/him.
Can you try the Police and Crime Commissioner for that police force also?
Do you have a solicitor? If not, then get one pronto. Crowdfund for legal fees.
Have you considered contacting a journalist? This is a hot topic at the moment and I reckon a few would be interested. If this went public on Twitter then, based on what has happened previously, the police would be forced into making a statement of some description - whether that is good or bad.