Why should I be charged a restocking fee ($55) when an AT&T employee sold me the wrong phone?

Today I went into a corporate AT&T store and asked specifically for a flip phone that supports GPS. An employee I spoke to showed me the "Singular Flip", which had Google Maps. I came back later to buy this phone, but there was a different employee this time. When I said I wanted to buy this phone, the employee said she would be right back, went into the back and brought out a box containing a phone which I later learned was not the phone I asked for (the "Singular Flip") but instead the "TCL Classic" (I realized this when I was using it and saw it didn't have GPS).

I called the store from home about the issue, saying that I had asked for the phone that supported GPS, and the phone I was sold was not what I asked for. The same employee who had sold me this phone answered. She was apologetic, saying that they didn't have any flip phones with GPS at the moment and they only had TCL Classic. She suggested I buy one that supported GPS from another store and come back to return this phone.

I did end up buying an "Alcatel Smartflip" from another store. However, when I came back to return the TCL Classic, I was told by another different store employee and the manager that I would still have to be charged the restocking fee since I had opened the box and used the phone. I explained that I shouldn't have to pay the restocking fee because it wasn't my fault I was sold the wrong phone by the employee. They kept insisting that there is nothing they can do and that there is no way for them to waive the fee. 

I shouldn't have been sold the wrong phone in the first place. And I feel like the store manager was trying to take advantage of my naivety because I am young. But I know this isn't right.