When Property Changes Hands Are Tenants Who Signed A Lease With The Original Owner Responsible For Keeping The Lease When Expected To Pay Additional Rent Beyond The Lease?

My son and a friend signed a lease for an apartment in the spring for fall and spring semesters at college 2007-2008 at $1000 per semester for each and $250 deposit for each. The deposit was paid and the lease signed. The apartment was sold and the boys were contacted that the rent was now $1800 per semester. We asked for the refund of the security deposit because this was not what we agreed upon on the lease and were told they would not refund it and we would have to pay for the first semesters rent.