Stuck with an upgraded cell phone plan and no phone

[kap]

S/O and I are on a family plan. Our contract expires this month. Last month I tried a new phone and upgraded my plan. I didn't like the phone and decided to wait until the end of this month. On my behalf, before the 14 day deadline S/O returned the phone to the ATT store (not a mall kiosh) where I signed up for the upgrade. Now that we are both ready to renew our contract with the new phones we like, ATT customer service reps told us that I cannot because my plan has already been upgraded! I told them the story. They said there is nothing ATT can do. Neither is ATT responsible for independently owned stores! I have to prove that the phone has been returned to the said store and the salesrep must call ATT to confirm it. Calls to the salesreps have not been returned. Now I am stuck with a new plan with no phone. No docs were given to S/O when she turned it the phone. So I have no proof. What to do? Any idea? TiA