Refusing to replace under warranty battery

I took my battery in over the weekend, as it just went flat, I had it tested by a qualified external party which even gave me test results stipulating that the battery was dead and needed to be replaced. I went to Battery Centre, where they first came with the story that my battery, which was still under warranty, was not tested correctly. After testing it, the person who assisted me said that it was only flat, they will recharge it and I could pick it up on Monday. Monday afternoon I went to pick it up and they stated that it was not flat, but broken. No one called me to tell me anything. When I claimed it was still under warranty, they refused to fix it, as suddenly the poles where bashed in, and they claim that I hit it with a hammer. There was nothing wrong with it when they took it in for a recharge?? Is that the way they do business, by damaging the battery so that I am denied a replacement? It is not acceptable at all. Very Very unsatisfied.