Mortgaged room for rent was sold by the owner without my knowledge.

A 'room for rent' was mortgaged to me last feb.2011.The owner & I had a written agreement(without notary) that the monthly rental fees would be received by me until the time the said room is redeemed by the owner by giving me the exact amount of the mortgage.For the past couple of months(from March-August)the owner was faithfully giving me the rental fees.But last week,I discovered that the owner alledgedly sold her entire house & lot(including the room for rent mortgaged to me) to her sister,without my knowledge.Now,my problem is the alleged new owner already destroyed the entire house(including the room for rent mortgaged to me)and is planning to build a new house.How can I recover my money I used in the mortgage?By the way,the said room for rent was located in the ground floor separated from the main house.