Charge off Issue, how do I fix it?

I am trying to get a charge off removed from my boyfriends account, he recently went to refinance his home and we were informed that we were unable to due to his credit had dropped immensely. He had two charge offs for the same account number showing. What had happened was he had a loan on a truck, the truck was stolen and burned. The insurance company investigated the claim for 6month. After six months they paid off the truck loan, by this time the loan had gone into collection. We were not informed that the loan was being taken over by collections, no late notices were sent in the mail. After the insurance claim we thought the insurance company was to take care of all matters pertaining to the truck. So I sent out a letter to each credit company and received a letter back from each, the duplicate was removed from two of the companies and the 3rd wrote back saying they felt like they had received a fraudulent letter. I did not get the letters notarized and I did not send the letters certified. What should I request more specifically in my next letters I send out (which will be notarized and sent certified) to get the companies to fix this error? It is hindering us from being able to do just about anything!

Thank you!