How can the family of the deceased receive the NOC ?

Dear sir, My Uncle's only son who was married having two children both minors, died in a road accident on 16th September 2015, he was the only bread earner of the family. He had a commercial vehicle(10 wheeler) financed from Sriram Transport Finance Company(STFC) amounting Rs 5,05,000 approximately, the vehicle was insured under Shriram insurance for credit life Insurance(body insurance) after 3 months of the incident the Insurance company paid a sum of Rs 3,76,000 approx as credit Insurance to Sriram Transport Finance company. Now when I approached the Finance Company(STFC) for the NOC they are saying that some of the premiums were not paid by the deceased before his death on 16.09.2015 so his family have pay the due amount to avail the NOC . The amount due as per their account varies each time I visit their office for negation they started with an approximate amount of RS 3,80,000 and now they say that the amount is Rs 6 lakhs and over. The company has never in the past 18 month intimated in written, called over the telephone or issued any notice in this regard, each time we have to reach them for negotiation they do not show any short of interest in this matter. As I earlier said the deceased was the only bread earner of the family his widower is not in a situation to pay any amount still she promises to pay a sum of Rs 1 Lakh to the company the branch Manager says it is not enough and that she needs to pay the full amount in order to avail the NOC. I request you kindly to suggest some legal measures that can be taken so that the family of the deceased can get the NOC. Thank You