What can my friend I do .he paid for health insurance for coverage ,but they did not pay on any of his medical bills from Dec1 2016 -Aug 2017

He is disabled thru his company and had purchase another insurance company after his insurance with his company expired..On Dec 1, 1016 his new health insurance took active. On July 13 ,2017 he received a letter from the insurance company that he was cancelled on December 1,2016 ..the insurance company took his payments and had approved for all medical treatments. They have caused him approximately between 30,000 -50,000 if not more in debt..he has been placed into collection and possibly further in time Court issues.. They have caused emotional stress and harm to him... Had he been informed he could have found another health insurance coverage before these damages ...