Why is my trade-in value. not showing saying that I owe full price on the phone. they already verified my $800 credit and gave me my new phone

Yesterday I went to T-Mobile and was added to my friends plan. I traded my iPhone 1160 for you right and was given an eight hour credit, that’s even better for entire bill for two months but it’s not what we asked for 30 minute thing, and my new iPhone is showing me that I haven’t even paid installment yet and has the full verse there. I have an articles about T-Mobile doing this and I will Presley correction if we do not get to the bottom of it. My phone is to me five dollars and some change every month plus $48 insurance at my service is only $20. Maybe 30 tomorrow I would like to six probably before and up keeping the phone and getting it unlocked since my money was basically stolen and put towards something that I did not say/was even asked if that’s what I wanted to be done with it. The weird part is that it is showing credit on the bill I was assuming that was left over but my phone whichever 50 times was covered except for the five dollars and some change a month asked me to know insurance in the service but that is quite a few lines of a plant. I need an email  back promptly.