Was this is a true story?

I don't think it was a strictly true story but one based upon a synthesis of ongoing insurance companies abusing its insureds. As a true example, a few years ago there was a company in Louisiana which was selling minimum coverage auto policies but would not pay on any claims without trial, regardless of merit, to delay payment. When it came out what was being done, the company filed for liquidation and so the claimants got pennies on the dollar through the insurance guaranty fund (to which all carriers pay for situations where companies go belly-up, usually from mismanagement rather than looting like in the movie and in this case). The company owner was caught fleeing with cash and was jailed. Coincidentally, the elected commissioner of insurance, who got big campaign funds from this insurance company owner, was unable to find anything wrong with all claims being denied until the proverbial stuff hit the fan. The commissioner was voted out next round. So for those who don't believe the storyline, they are out there.
A national story like the abuse in the film: look at UNUM/Provident disability which agreed in November 2004 (due to a similar pattern of denials without any basis) to pay a $15 million fine and another $150 million payment if they did not correct their procedures. Can you imagine the pain of finding yourself disabled with bills coming in but no income only to find your carrier is denying claims wihtout any legal basis as a matter of corporate policy? For instance, the company hired doctors who were denying disability without even seeing any medical reports. The case was brought by all of the 50 attorney's general in the USA. You can find the settlement by googling the case.