1) SI shoukd have lodged FIR on your complaint of criminal trespass and criminal intimidation under section 441 and 506 of IPC
2) mere warning is not sufficent
3) lodge complaint against SI before the commissioner of police for refusal to register an FIR
4) if no FIR is regd you can lodge private complaint with magistrate under section 156(3) to direct police to investigate and submit report