Hanging up on your customers is how you solve your most complicated problems

I have spent the last 2 hours on the phone with multiple representatives trying to purchase this phone. 

https://www.att.com/cellphones/samsung/galaxy-s7-edge-used-phone.html#sku=sku8370477

Once I log in the website insists that I add another line instead of allowing me to upgrade my phone to this model. My first call experience forced me to walk through all the troubleshooting that I had already done with someone who clearly did not understand the issue and could not help me. I finally get them to transfer me to their supervisor, to whom I calmly explain the issue and ask to be put in touch with the right person. When I am transferred to a competent person who understood the issue, they hang up on me. I had to call back and go through this hour long process AGAIN. This time when I finally get to speak to a competent person we walk though every possible scenario and they decide they will escalate the issue to the proper person. They PROMISE to connect me to someone who will understand the issue and have it explained to them before I talk to them so I don't have to explain it for the 7th time. Instead I am connected back to customer service call center and of course hung-up on soon after. I was never once rude, I just presented a challenging problem that 7 of your employees couldn't handle. My dad worked for AT&T for 36 years. I am going to pass this experience on every social media outlet and promise to bring this up every time AT&T is mentioned for a long as I remember this day. It's a website issue, and your All I wanted was to buy your product and you managed to turn it into a negative experience.