Midas fair deal nothing fair or honest about them

I recently bought a battery and service kit for one of my vintage cars. I told the service guy the make and model and year. And then asked for that exact service kit and a new battery. When he put the battery on the counter I inquired that it looked alot smaller then the one I was exchanging. He gave me some schpeel that they are made smaller now. I'm not a full fledged machanic. And learning on my cars as a hobby. So I trust the parts centres for advice. I fitted the battery. And still had issued with her starting. After a mechanic mate came over to look. He told me the battery is too small. I called Mercedes Benz and asked. They have me the size of the battery that should be in the car. I called Midas first, told him they sold me the wrong battery. He said come in and we can look at it and exchange it. Which I did. But once I was in the store their tune changed. They first told me the battery was damaged which it not. Then said I asked for that size. And never mentioned the service kit. I showed him the slip and he bluntly refused to exchange the battery. My thoughts are this. Many people do DIY services on their older cars. And if this is what these so called professional suppliers are doing and then refusing to accept their own mistakes. How are we supposed to trust them. I have told all my vintage car owners to avoid this store and not support him. Rather go 2 kms down the road to another auto parts shop and support them. They helpful. They have no issues exchanging parts. And have twice admitted to giving me incorrect parts. Exchanging them with no issues or surcharge