Car Rental Nightmare

I got a rental vehicle from Avis through my Insurance MiWay for after I had to take my car in for accident repairs. When I returned the car at before the date of expiration, Avis told me I was meant to be charged for an extra day off hiring, personally and not billed to my insurance. When I explained to the agent assisting me that the vehicle was even brought back before the date of expiration he did he sort it and call me back I should leave the car. I had to call Avis the next day to find out if the matter was resolved and enquire when I'd be receiving my money back, I was told by the consultant that everything was resolved and my money would be in my account in 5 days. Much to my horror when I found a charge from Avis for more money and no payback