Being charged for the wrong phone model

I bought my Galaxy S6 Active back in August and never really checked it like I should have. I'm doing AT&T Next 24 plan and I ordered the 64GB version. Well, in January I was looking at my storage and noticed that it said 32GB which is not what I'm paying for on my bill. Well, I couldn't get the time to go to the store since they close around the same time I get out of work. Finally, around last month, I contacted support through Live Chat and they told me I would have to visit the store to get my bill fixed but they offered me a $10 discount for my last bill.

Finally managed to get to the store today and the manager first accused me of switching the phone and then after checking IMEI gave a surprised reaction and decided to tell me that the price was correct because it's the old price for that phone model. I tried to have a conversation with her about the issue but she kept pointing at my original receipt (which does not show the memory size) and saying that if the price is on the receipt then it's the correct price. She kept saying that the price is the old price of the phone even when another employee tried to show her the price difference in models (it's easy to look up the price of the phone back then and check). She quickly walked away and left me with another clerk (I was there getting my wife a phone, decided to take care if the bill issue finally) and that was the last I heard from her. As i wad leaving I was told that that the general manager was on vacation and that I would be contacted when they got back.

I'm doubtful that I will get a decent outcome and I'm already at the point of just giving up and just keep paying my bill. I did do some research and I do in fact know that the 32GB version was $594 and not $694 like what I'm paying right now.

So, besides waiting for a call from the general manager which may or may not come. Should I just make a claim with the BBB as well? Or trying online/phone support again? The monthly cost difference is only $4 but that does equal to an added $100 overall that I will be paying for a phone that I do not have.