Mobile shop wireless

My daughter purchased an *** from this company for $500.00. The guy told us it was brand new and now after 6 months of having the phone it stopped working I took it to Metro to find out what was going on and told told me it was list as lost or stolen. So I found out who the carrier was for the phone and they told me that they phone was shut off because the person was not making their payments on the phone. I ask them to tell me how much they owed so that I could pay it off but they couldn't tell me, I also asked if they would buy the phone back from me they said only if it was paid off. I fell bad because my daughter saved that money up to buy the phone her self.I don't understand how a business can sell phones to people that are blacklisted because they are reported lost or stolen or sell you a phone that bought from someone and sold it to us probably knowing that this would happen.