Can an old landlord go after me for rent after a 30 day notice has been submitted?

I had a lease with a particular (shady) Los Angeles Management Co. from October 23, 2005 to October 23, 2006. Due to irreconcilable differences with my former (flaky and overall manipulative) roommate, I moved out on November 25, 2006. I sent them the notice to vacate on October 8, and rent was paid in full. When I later called to confirm its receipt, I was given the complete runaround. (I have copies of the letter and lease) After discussing the issue with an attorney, I was informed that once I move out I was no longer liable for rent on the apartment. I then proceeding with moving out. About three months later I got a call from the manager informing me that the rent was consistently being turned in late. Essentially, they are trying to go after me for rent on an apartment I no longer live in. I informed them that legally that it was not my responsibility and that they needed to contact the old roommate. They are continuing to contact me regarding this. What should I do?