Complaint against the retention department- Billing

I have been a long time customer with AT&T.  I recently, three maybe four months ago took advantage of my upgrade to the new Samsung S6 phone.  I have never had any problems with my phones in the pass.  This new device was just not working.  Then I spoke with representatives in the retention department just about every 10-13 days notifying them of the problems I was having with my new phone. So Mr. Frank a manager in retention stated that he could save me $20/month on my account. I asked if my plan have to change. He stated "no" he saw that I was paying $30/month for unlimited talk and text and he can take $20 off since I have 2 phones.  Not knowing that he changed my data plan. So last month my bill was increased $114 over for overages for talk/ I spoke to a Zackary on July 7, 2015, I explain my problem with my bill he assured me that the bill will be taken care of and was there anything else he can do.  I then went on to explain the problems that I have had with my phone. He then offered a free upgrade.  He asked me what phone I wanted I said the Samsung Note 4 edge. He then that he suggested that I should go with the NOTE 4 not the edge. I told him ok.  The next day I checked my account saw that my account was not credited for the $114.  After talking to a Yolanda and Nicollentia Johnson, Lakeia was the only representative that took the time to hepl me. Lakeia assured me that my account would be credited and it was. So once i received the Samsung Note 4 on July 10, 2015, and took it to the At&t store to activate my phone, I then asked the Representative what was the difference between the edge and the regular note 4 she stated that the edge is the newer model and that if it was her she would ask for the edge since that did a free upgrade to the NOTE 4. I called retention talked to Amber and she stated my account would be billed $99 I told her no I was told that it was a free upgrade.  I was told that it would be credited once At&t receive my Samsung s6. So when I received my terms and conditions I called back again to verified that i would not be responsible for the $199 and was told no… I talked to a Elisa.  She assured me that once both the Note 4 and the Samsung s6 was return it would be nothing added to my account.  On July 27, 2015 I talked to a Madison about my account billing for the month of August, i was charged for the $99, $199, $80 for upgrade fees/ so my bill is over $568 who said there was nothing she can do about my bill.  ...I asked if a manger could call me. I never received a call back. I call July 28, 2015, talked to a Alan in retention who had me on hold for 15mins if not longer and then was disconnected, called back talk to a Brianna who was very helpful she took her time to go through all my notes but then told me that my account was flag to not apply any credits. She stated that this was wrong and was trying to get a manger on the phone to go over my notes. I was then disconnected from her.  I called back and talked to a Latonia who told me that she will have a manager by the name of Deavanie call me back.  I requested that a supervisor review the phone calls from July 7 till now.  Retention has made it very difficult for me to get help.  Some of the people are not documenting what they are advising the customer on the phone therefore flagging me.  I don’t appreciate the help or the lack of I have received.  All I want at this point of time is for my bill to be corrected. My bill should be no more than $160/month. I have a working phone finally.  SO PLEASE HELP!