faulty car battery with no results on the problem

My Willard battery has started giving problems by not starting the car. So I took it in to Midas Wierdapark where they assisted me by giving me a loan battery, after a day or 2 they phoned me and told me that I have to bring the car in for them to test the alternator, because the rep of Willard doesn't want to give a replacement battery unless they knew the problem was not with my car. I took the car and they tested the alternator and it is working 100%, so the problem is not with my car. After the test they said they will come back to me. As if yet I haven't received any feedback. Everytime I phone to find out what is going on, they keep on saying the rep is not there and will phone me back. But they don't phone me back and I have been repeatedly phoning with the same results. It's been over a month now, I am using the loan battery but the battery is much smaller than what my car needs, which is still resulting in problems for me everytime I need to drive.