Terrible Customer Service After 17 Years

I have been with T-mobile for seventeen years. In the beginning the customer service was acceptable, then a couple of years ago I thought the customer service was the best I was getting from any business I deal with. I always spoke on the phone to someone located in the state where I live. But the service is terrible now. Like almost all customer service departments it is located in the Philippines  or some other foreign land and I can't communicate with most of the agents. I don.t understand what they are saying and they don't understand me. For a couple of weeks now I have been trying to trade in my phone. TM says I can trade in for free. But every time I  talk to an agent they e-mail me a contract to sign that says I will be billed payments for 24 months but they won't put anything in writing for me saying that they will give me credit for the same amount for 24 months. They expect me to put it in writing that I will pay them but they also expect me to trust them that they will credit my account every month. I refuse to sign the contract unless it states that they will credit me or else that I will owe nothing for the phone as long as I stay with TM for two years. They don't trust me but I am suppose to trust them. I went into a corporate owned TM store in Saint George, Ut. about a week ago to discuss this with them. I was told by an employee at that store that he would have everything in writing for me to sign that states the I will be credited.  That sounded fine.  I went back to that store yesterday and he was not there. Some other employees were there. They treated me like crap. They had rap music blaring and showed me something in writing about getting the credit but told me I would not get to sign it or get a copy of it no matter which phone I traded in for. I wanted to point at something on one of the guys screen and he rudely said to me "Don't touch this!" Very unprofessional and rude people working in that store. They should hire a better class of people to work in there. I went out to my  car and called customer service again and went over everything one more time with another agent. She said she would e-mail me a contract to sign stating that I would be billed one time for the phone and I would be credited one time for that amount. After being on the phone with her for an hour I received an e-mail for the same 24 month billing and saying nothing about credits. There is no phone number to call about problems or complaints. All of the phone numbers posted online just take you back to the same recording that takes you back to customer service in another part of the world. I called a number that was supposed to be TM's corporate offices and a live woman did answer but she just transferred me back the same recording that takes you to customer service. They don't even have an e-mail address to contact someone about your concerns.  They don't want to hear about it. After 17 years I am looking in to switching carriers.