Only paying for partial repairs after accident

Recently my wife had an accident in our car, with damage to the front of the car. Everything went smoothly up until the time I was told I could come and pick up my car. Getting to the panel beaters the car was running, and the repairs looked great. I'm very happy with the work they did. But then they told me that I won't be able to start my car after I turned it off, because the battery was damaged and doesn't charge. When I asked them why it wasn't replaced they told me that they did submit several requests to Outsurance, but that Outsurance refuses to pay for it. The assessor claims that the battery wasn't damaged in the accident. When I opened the bonnet, even I could see that there was clear damage to the battery, it was bulging on the side. Now Outsurance expects me to take my car home, more-or-less fixed? Trying to deal with their complaints department is not bearing much fruit. They want a receipt proving that it was a new battery. Not that it should matter if it was a month old or 10 years, it was working before the accident, and now it isn't. I only got the car 1 June 2015 from the dealer, now I have to beg them to find that receipt. All this while sitting without a car.