Lease My sister just renewed her rental lease and moved into a 2 bedroom apt…

Lease
My sister just renewed her rental lease and moved into a 2 bedroom apt in the same complex. The lease was written for &760 mthly. One 3 occasions she brought this price to the attention of the management office and asked if it was correct, each time she was assured it was. She has since moved into the apt and been there for over a week. Now she has receieved a call saying the rent is $950 and she needs to sign a different lease. Isn’t the lease she have a law binding contract and shouldn’t it have to be honored by the apartment complex? What legal grounds does she have or does she actually have to sign a new lease? We appreciate any insight you can give regarding this matter. Thank you soooooooo much in advance.