What to do if police refuses to register FIR?

I seek legal assistance to initiate action against an individual involved in multiple serious cognizable offences. The matter includes sexual harassment, attempted rape, physical assault, and blackmail through private videos, causing severe harm to the victim. The accused has also engaged in online defamation, filed false complaints to harass others, encroached upon SC/ST land, caused environmental damage through illegal activities, and violated labour laws. Despite reporting these incidents, the police have failed to register an FIR or take action. I seek guidance on the most effective legal strategy to ensure FIR registration and proper investigation, including remedies under Section 156(3) CrPC. I also request advice on invoking relevant legal provisions, approaching appropriate authorities, ensuring victim protection, and preserving crucial evidence to build a strong and sustainable case.