Can I use RTI against my insurance company?

Only partly. The RTI Act is not the legal basis for fighting a rejected claim — use the GRO, IRDAI and Ombudsman route for that.

RTI applies only to public-sector insurers (which are public authorities) and only to obtain information. For a private insurer, RTI does not apply; use IRDAI, the Ombudsman, or the consumer commission instead.