horrible customer service

After 6 months, still no resolve.   i purchased two new phones in June.  during that transaction, one phone was completely correct with the trade-in and billing.   the second phone has not be corrected.   At that time I was informed the trade in would be $200-300 and my device dollars would be used.   Since then, after multiple calls to the authorized retail store,  no resolve.   I keep being informed that the district representative has all my information for the trade in and "it will be only a few days for a decision".   No decision has been made, or should I say, if it has, no one has told me of the result.  Secondly, the device dollars and their use... I already escalated that via telephone call to an agent last month... still no use has been noted.   How do these stores keep being allowed to promise things, underdeliver and stay functioning?   I work with the public every day.   In my job, which is health care, if I were to underdeliver, people can DIE.   So, i know how to deal with the public.  Do not promise anything that you cannot deliver.   AND, if you do promise, don't keep pushing off the issue until you think the person will just drop the matter.  I have been a loyal customer for over 15 years.   Including this upgrade, this is the third time I have had issues with the costs and little to no satisfaction/resolution without waiting multiple months and multiple complaints being filed.  IS THERE ANYONE THAT CAN HELP ME?