Yes, certainly it is legal and your right as per policy conditions.
But u cannot claim for the amounts u have already received from one insurer. The reason is simple:-
Mediclaim policy of General insurers are reimbursement policy pertaining to medical treatment undergone by the insured members (with cashless facility now a days).
Health Plus policies issued by LIC are non-reimbursement policy. In other words, they don't entertain medical expenses but provide Hospital Cash benefit and Major Surgical Benefits as per the policy terms and plan opted.
Hence u may call for cash benefits from LIC if at all the no. of days spent in hospital has crossed the days of waiting period as per health plus policy.
Apart from the cash benefit u make also claim for Surgical benefits if the surgery undergone by you falls under the Major Surgical list of LIC Health Plus policy.