Can insurers reject claims and deny payments

Can insurers reject claims & deny payments on the basis of late intimation?My mother passed away around six months ago. She died in an unfortunate accident where she fell off a two-wheeler vehicle & succumbed to a severe head injury (At the time of the accident, the vehicle was being ridden by my sibling & my mother was riding pillion). My mother held a health insurance policy that offers a fixed monetary benefit in the case of accidental death. I am the only nominee to the said policy. She also held a PMSBY government policy, which too offers a fixed monetary benefit. I am the owner of the said two-wheeler vehicle & have an own damage insurance policy against the vehicle, that includes “Unnamed PA cover” which offers a fixed monetary benefit against accidental death of pillion rider. My brother is the only nominee to the said policy. The issue is that it’s been more than six months & we were not aware of such benefits being offered by the insurers until now (The broker through whom we had purchased our mother’s health insurance policy also didn’t inform us about the benefit). Though we have intimated the insurer with whom my mother held a health insurance policy but only to claim reimbursement of the medical expenses that occurred during her hospitalization & not to claim the fixed monetary benefit being offered by the insurer (The reimbursement process hasn’t completed yet as upon submitting the necessary documents, the insurer provided us with another & a long list of documents that we need to furnish further in order to receive the payment and we are yet to do so). The other insurers haven't even been intimated yet. So my question is, can the insurers reject our claims & deny the payments if we raise them now after such a long period? If they do, what can we do to receive the benefits? What does the law say about the same?