Landlord sold house.New owner demanding late rent.....Is this legal?

My landlord was having his house foreclosed.We worked with him to help him catch up with his mortgage so he could keep his house.We borrowed $5000.00 from relatives in exchange for another years lease.In return, we found out, he never paid mortgage with the money and was still in foreclosure.We refused to pay anymore rent.It is now 3 months later and he just sold the house this past week to his ex-wife .We received a quit from the new owner today demanding the 3 months rent I owed the old landlord.Why do I owe her money when I never heard of her nor never knew she bought the house? I didn't owe her the money..I owed the old scumbag landlord the money.Am I going to have to pay her for the late rent? I don't think its right that he conned us out of $5,000, kept the money and now we'll be out in the streets........