Unresponsive Customer Service - I need a refund for returned phone - Who else can I talk to?

Hello,

I have been back and forth with AT&T for months now and I'm at my wit's end.  Back in August, I ordered a new iPhone online.  Unfortunately, my existing phone stopped working entirely before the new one was delivered, and I had guests coming into town so I needed a new one immediately.  I went to my local AT&T store in Willow Grove, PA and spoke to representative who sold me a new phone and told me that when the phone I originally ordered came in via mail, I could bring it to the store and they would handle the return.  Both phones were bought for the full price of $700 and I was told when I returned the phone I'd get my money back.  When my phone was delivered the next week, I brought it to the same AT&T store.  A different representative told me that I was not supposed to take it to the store, but rather should just send it back via mail with the label provided to me in the box.  He went to the back and got some tape and taped the label to the box and sent me on my way.  I dropped it in a blue mail box at the Abington, PA post office, and no one has seen or heard from it again.  I checked my credit card account daily to see if the $700 was refunded to me and it never was.  I initiated a handful of online customer service chats, and during each one the AT&T representative promised me an email with an update on the missing phone.  I never got any emails.  One online representative even told me that the phone was returned and that I'd see the money back in my account in several days, which never happened.  I then started calling, which is very difficult to do for a person who works during customer service business hours.  I had 3 separate phone calls that lasted about 2.5 hours each and got me nowhere.  I was scolded for not having the tracking number, which I admit I should have written down, but I was surprised that even though AT&T provided me with the label, they were not able to find the tracking number either.  I told the same story to at least 20 representatives who each told me that a different department was better suited to deal with this and transferred me off.  Sometimes during the transfer I was disconnected completely and had to start all over again.  I opened an official investigation with a ticket number, and after several days I received a text that it had been resolved.  When I called to find out what the resolution was, the rep told me they couldn't tell why the case was closed, opened up a new one and transferred me to someone else.  I spoke with a Candace Charles who told me her manager was Aaron Webb and promised me that she would call me with any updates; she never did.  I finally spoke to a rep named Michelle who gave me her direct number and promised that she would follow the case closely and keep me updated.  At first, she was very responsive and helpful.  I have since left her 3 voicemail's to which she did not respond.  If my phone never made it back to AT&T, I do not believe I am at fault, as I followed all instructions as they were given to me.  I would really like my $700 refund and I don't know who else to contact.  Does anyone know if there is an upper level manager to whom I could send a letter?  I have been a customer for over 10 years and I cannot believe that I've had to go through this nightmare.

Thanks,

Emily