Can a property management company charge you for the remainder of a lease if they have rented that apartment out?

I unfortunately had to break a lease due to lose of a job. I was under the impression that they can not charge you if they have already rented the apartment to another person. I am being charged close to $8000 because I signed a 2 year lease. Typically I would think 2 months would satisfy. I left the apartment immaculate and wasn't charged for anything but the unpaid rent. I thought I had read this under Nevada real estate statutes. I acted quickly in signing the lease without realizing that the entire lease amount would be asked. Then I also received a letter stating if I don't reply in 10 days and pay the amount they would charge me 3 times the amount. So the amount is actually higher than this because I obviously do not have $8,000. My husband was also berated on the phone by a supposed lawyer, I think is a bill collector calling himself a lawyer. He called my husband a Mother F Doesn't seem reputable. Thank you