Help!!! My Auto Insurance Company is refusing to cover my rental car!!!?

I am insured by USAA & have been for over 12 yrs. A few months back I was involved in a hit and run accident. I did not immediately notify USAA of the incident because I did not file a police report at the scene and I didn’t know if the car was even repairable and just a few weeks prior to the accident I had just reinstated my policy after letting it lapse because of being laid-off and not having income. After notifying local Police I was told that in my state (TN) that if you don’t file a report at the scene of the accident you can not get a “delayed report”. At the time of the accident I could not get the drivers tag # because of him fleeing. So after talking to friends, family, and a police officer friend I decided to file the claim. All the while my car was sitting at the wrecker yard. I contacted USAA two weeks after the accident & gave a statement. They moved my car from the wrecker yard to a USAA approved shop where it was deemed a total loss. Now let me also say that approx a week before the accident I had gone into a rental car company and rented a car for my Brother who is not old enough to rent one himself (19) you must be (21+). I rented the car in my name and listed him as a secondary driver. He is also insured by USAA so he’s covered for any car he might drive. He personally does not own a vehicle and had gotten a new job so he needed a way back & forth from work temporarily until he could work something out. So the afternoon of the accident I contacted the rental car co and explained that I, myself had been involved in an accident in my own car and that I was going to need to keep the rental car but wasn’t sure for how long. I told them that it was going to be an insurance claim and that I would pay for the week and one day that was not insurance related. So from that day forward USAA should have picked up the tab for my rental car because I have rental coverage/reimbursement on my policy. USAA sent me some paperwork to sign for my title and told me that once they received it that they would release the settlement check into my account. After not hearing anything for 5 days I contacted USAA & was informed that my claim was sent to their Investigations Department. This enraged me because no one had called to question me or inform me that the claim had been halted. I finally got in touch w my Adjuster and she said the reason it was being investigated was because of the date I got into the rental car and that an Investigator would be contacting me. So three days later I get a call from this Man and I agree to meet him in person to explain the dates and why I rented a car a week before my accident occurred. Had I known that by me renting my Brother a rental car in my name would have caused all this trouble, trust me, I wouldn’t have done it. When I met with the Investigator he was mean and interrogated me like I was some kind of criminal. I know that’s his job but let’s be honest, If I’m going to try & pull insurance fraud it wouldn’t be on an older car that’s paid off and is over a decade old. With all that being said the Investigator took over three weeks to complete his investigation and sent my info back to my Adjuster who by the way told me that if they did decide to cover the claim they were NOT going to cover my rental car. No one from USAA called to tell me that the claim was going to be covered and that the investigation was complete. I had to contact them relentlessly until finally I spoke w someone that simply said “Ok, looks like everything’s good to go. You should see the $ in your account within 5-7 days”. They kept horrible communication with me, the insured. They did finally put the $ into my account for the value of the car but I’m still out all of this money for my rental. It wasn’t my decision to investigate the claim, it was theirs and they drug their feet for over a month to settle this claim so they should be responsible for the rental because I have the coverage on my policy. If someone could please give me some suggestions on what I can do or what my rights are as the insured I would greatly appreciate it. Thanks so much!!!!