AT&T Trouble Getting Answer to Returned Item Issue

Hello, I have the Family Plan 20 gb wireless plan.  I had an issue earlier this year where AT&T provided me a phone case which I received in the mail.  It was not the phone case I asked for so a representative told me to return the case and I would be given a $50 credit + tax back on my next bill.  It has been over a month since it shows returned and I still do not have the credit.  I have spent over 5 hours talking with AT&T representatives just to be disconnected from on AT&T Chat or even worse, over the phone, I have been continuously transferred to departments.  The one time on a call they transferred me 5 times before I hung up, and one of the transfers went to an analyst feedback team that had absolutely nothing to do with my situation!  This is getting way out of hand and I need help figuring out how to fix this issue.  All I want is the credit so I can buy my own case and move on.  I would love someone who can actually help to reach out to me.

I have an AT&T Chat saved where the representative promised that I would receive the credit.  I even sent it to one AT&T representative and they still denied that anything was in writing.  This is getting out of hand, please help!