With ANY and I mean ANY call center, right off the bat, ask for his/her supervisor. When and if they ask you whats wrong, tell them you need a supervisor, no other questions should be asked. Once a customer asks for the supervisor, they by law, have to trans you to the supervisor. Make sure you get Reps ID number and name. Tell them whats going on. Personally, I like to put Tmo supervisors on edge and tell them, "Well I could go to Sprint (or any other company) and get great service everywhere." They tend to tell you that they are working on towers in that area or that they will put a ticket in for you. Ask for the ticket number and a phone number you can call and find out whats being done to resolve it. And if none of that works (which it should, I use it everytime I call!), you want a name and number for the CEO. That will make them pee their pants.
This by the way, is experience in calling CS and working in one for 5yrs. Believe me, tier1, 2 & 3 reps don't give a flip about anything besides when their next break is!
Good luck!