@JCAEA,
JCAEA wrote:
She gave me permission to leave end of December
What does that mean? Did the landlord agree to terminate your lease? If not, then you were still responsible for the rent for the remainder of the lease term. When a tenant abandons a lease, the landlord is entitled to rent out the property to a new tenant, in which case the old tenant's responsibility for paying rent would be terminated (subject to certain conditions I won't go into). On the other hand, if the landlord is unsuccessful in finding a new tenant, the old tenant still has the obligation to pay rent.
Sounds like your landlord took your security deposit in lieu of rent, which probably means that the lease was never terminated. You left, but you were still obligated to pay rent unless your landlord found a new tenant. That didn't happen, so you were still on the hook for the rent. When you didn't pay, your landlord took the security deposit. End of story.