Sounds like the Apple reps put you on EIP. You have to take it up with the Apple employee that did your transaction.
I agree with tidbits. It sounds like you're on EIP and still being charged for the phone you traded in with the Apple Upgrade program. You're not the first to experience this as I've heard of this happening a time or two. Have you already talked with Apple about this? They need to update everything on their end to close out the billing for the previous iPhone.
T-Mobile people are lying idiots. You should cancel and use another carrier.