Being charged for a free phone

I went to t-mobile to originally downgrade my plan but I was offered $1000 off the new samsung s24 if I upgrade my plan. I repeatedly asked if the phone was free and if I was gonna have monthly charges for the phone and the representative kept telling me my bill will be the 150 and nothing else. That the phone was free and I only had to pay activation and taxes. Okay, cool. My bill came in today with me paying off the phone!!! After I was told my bill wouldn't be different and I wasn't going to be paying off the device. Why was I lied to!?