ATT won't send new replacement phone

I recently bought my son an LG V30 through the upgrade service ATT provides. Well, the phone happened to be a used item and had defects so we had to return it and wait a whole month so we can get the replacement. A month goes by and they completely mess up our whole order and now they're saying they can't send us a replacement because we don't have the upgrade anymore. I'm still being charged for a phone I don't even have anymore, I sent it back to their warehouse so we can get a new one. How is it possible that we don't have the upgrade when we don't even have a phone. My son has no phone and 6 hours on the phone with customer support did nothing to solve it. I was even hung up on by the supervisor! I just want this resolved so my son can have a phone. Please help me get the replacement I'm entitled to receive,