Worst customer service

I have been a customer for 16 years and am appalled at the lack of response and service I have experienced with T-mobile. I was due to receive a return call on Thursday 8/29 regarding an escalation or investigation on my account. When T Mobile merged with sprint I continued to be charged for a device leased with sprint on 7/21. That lease agreement was for an 18 month period. My account continued to be charged 45 dollars unbeknownst to me for a device that was paid off. In dealing with another issue I saw the charge on my account and spoke to customer care. The total amount of charges post the end of my lease is estimated in the amount of 900$. I was informed T mobile could issue me a three month credit only. I requested that the three month credit be issued immediately. In addition to my request for a full refund credit to be escalated to corporate and investigated. I was reassured I would receive a call back on Thursday from Monique regarding details of that investigation. I never agreed nor signed any agreement whatsoever nor did I receive any notification that I would be billed for a leased device post the 18 month period. No one has returned my call nor was I issued an immediate 3 month credit as promised. I am again asking this matter be escalated. T-mobile makes billions of dollars in revenue from its customers. If this issue is not resolved promptly I will be seeking consultation from an attorney to look into whether or not T mobile is stealing money from its customers and refusing to return calls or refund monies that are owed to its customers. I am asking that my complaint is further escalated and forwarded to the appropriate administration. Not a customer care representative with limited experience, capability, or scope to handle this concern. Please review the last call that was recorded and noted on my account. I am requesting a return call from someone in administration as soon as possible. I am also requesting my account is credited immediately as promised. Gracias.