Are there any remedy when an insurance company refuses to pay ADD benefits?

If the insured had a life policy with an Accidental Death and Dismemberment rider and the insured either died in an accident as indicated by the medical examiners report and the death certificate, or was dismembered as covered according to the definition of the policy, than yes, there is recourse. An insurance policy is a contract and therefor legally binding. But you do not have any recourse if the incident is not covered as described in the policy.