Disappointing and Unreliable iPhone 11 Battery Charging Issue

I have an iPhone 11 and an iPhone 6 Plus. I use the iPhone 11 at work and the iPhone 6 Plus at home. I charge them both with the charger that came with my iPhone 6 Plus. But my iPhone 11 stops charging on its own at 80%, 73%, and 94%—it won't charge at all. I told Apple about this problem, and they said that if my battery was in good shape, it could be because of the battery protection feature. I did what they told me to do and turned off the feature, but the problem didn't go away. They told me to wait a week because they thought it would get better on its own. After a week, my phone still isn't fully charged. Today, I called live support again, and the customer service rep kept saying that it was because of the weather and the heat. I told her that I work in a room with air conditioning and that the phone doesn't get hot. Also, the iPhone 6 Plus doesn't have this problem; only the iPhone 11 does. Even though I tried to change the subject, the representative kept talking about the weather. They don't seem like they want to help or find a solution. I hope they can fix this problem instead of trying to get me to buy a new phone.