Promotional Trade-In Credit Never Applied to Account?

I am going through this right now. I went through my app on my old phone under my login, went to upgrade, when asked about trading in my phone, I marked yes and they valued my phone at $800. When I get my bill, it shows that I am to make monthly payments when I was told that with my trade in and down payment I wouldn't have a monthly payment but would have a credit. Have got the run around for several weeks now and talking in circles. I call them out and demand for them to listen to the recorded phone call. Workers document different than what they tell the customer. It is ridiculous. Still working the problem. Not giving up