ATT cheating me out of my trade in reimbursement! I'm in Winston Salem, NC

After three months, AT&T suspended the reimbursement for my phone trade in.  I was on the phone for two hours, finally ending up speaking to a fourth person at retention, customer loyalty dept.  From what I gather, they said that the phone I sent in did not have the "where's my iPhone" turned off.  That is an outright lie, as I handled that myself, verified that it was turned off, and completely wiped the phone/reset, etc before mailing it to AT&T. I received two of the 36 reimbursements but then this month (January) it was gone.  So just like that, some (Edited per community guidelines) determines that.  I'm at this point going to look for another service.  I've been a AT&T customer for over 20 years.  And they are cheating me out of $280 of the $300 promised to me when I purchased my new phone (and continued service)!  So when you think about it, I gave them a perfectly good, perfect working order, clean device, no problems, no previous repairs, pristine....and they lied about what they received, and gave me no recourse, no communication...  Nothing. And this is what you can expect from being a loyal customer.  Not to mention, that I've been waiting since June for someone to come and replace a broken (spliced) cable as my tv/internet/wifi is dependent on that.  I can count on every night my service cutting out for minutes at a time because they've never followed thru on a service order to get that repaired.  I'm not sure what to do.  It's a pain in the butt to find a new service, and we have new phones (less than six months old).  But on principle, I'm tired of AT&T scamming and cheating their customers.