How do I reactivate my phone?

I went to the ATT store in the Victoria Texas mall and they tried the old bait and switch maneuver kinda on me. I told them that I wanted to trade in my iPhone 6 for a new IPhone 7 and they were really nice and said "sure we can help you". So they take my information have me sign 2 digital signatures, "he" takes the wrapping off the box for the phone, I tell him not to take the wrapping off the box but he says sorry too late,and then tells me I have to pay taxes. At this point I remind them that I wanted to trade in the phone and the guy goes "oh yeah." He looks up the model and says we can give you 140$ dollars. I'm like cool, that works for me, I'll just pay the taxes with it and apply the rest to my balance. He says "you can't do that you have to spend the rest in the store today". I say, "is there any way for me to get the balance left over after taxes applied to amount for the phone". He says "no only a corporate store can do that." So I excuse myself and say I can't take the phone since I thought I would be able to put the money towards the phone and say ok thanks I'll go ahead and do that tomorrow then". Well apparently he had deactivated my phone and was set to activate the new IPhone 7. I think he conveniently forgot about the trade and intentionally had me sign the digital signatures so that I would be forced to take the new iPhone 7 and be forced to spend the money from the phone in store. It was a really bad tactic that will keep me from shopping there and I will be telling everyone I know about it. My question is, how do I get my phone to work again and how do I file a formal complaint with ATT about the questionable tactics being used at the Victoria Texas ATT store in the mall?