How can I contact Apple about a bad Customer Service experience?

Recently my battery, like many others, has been having some trouble with retaining charge. Mid-January I brought my iPhone 6 into the local Apple store at La Encantada in Tucson Arizona. There, I waited in line for a reasonable (for Apple) amount of time. However when it was finally my turn I was told that there were no issues with my battery by an employee named James. I disagreed by stating examples such as charging my battery 3 or more times a day and literally watching the percentage drain. He turned off the background app refresh and told me to wait a few weeks and see if that helped. I was skeptical as, though app refresh can strain a battery, it should not cause this kind of drain on it. Before I left I asked if it was still possible to order a new battery to which I was refused, saying that my battery was fine and there was no need to order one for me. I left the store frustrated, but did as he said and waited. Eventually I could no longer use my phone without the aid of a portable power pack, and so I scheduled online through Apple an appointment for a battery replacement, only to be told the day of that they did not have any available batteries, though the Apple website had said otherwise. I drove back up to the local Apple store after contacting customer service and being told they may have a few. When I arrived employee Matt was very polite and happy to help. He tested my battery and found it to be “consumed” then commented on the notes of the previous visit where my battery test had failed. When I heard this I was incredibly angry, as I had been told that my battery was “just fine” and even refused a replacement. I would like to inform Apple about this experience in the hopes that this sort of thing will not happen again to someone else. It is offensive to me that an Apple employee does not think me worth the time and effort to provide decent service and do the job they are payed for.