Question about mutual agreement to terminate lease early

[Sepid Pooy]

Hi, 

I am renting an apartment with a month to month lease agreement that requires 30-day notice to terminate. I have moved out of the property due to an emergency health issue to live with my parents. I described my situation for my landlord in an email and asked to terminate the lease early.

He replied back with sympathy about my situation and wrote: "You may end the tenancy end of this week"

Therefore, I rushed to move out and dump all of my furnitures and house hold goods to meet this deadline which was Aug. 1st.

However, after I returned the key, the landlord is refusing to refund my security deposit because the lease agreement that I signed need 30-day notice to terminate the lease. I was wondering if the mutual agreement between landlord and tenant to terminate the lease early in email conversation has a legal binding to over-ride the 30-day notice requirement of the lease ?

My apartment was in Contra Costa County CA.