Lease renewal question?

[Bob Dole]

I have tenant move out of a rental one month early and without a written notice to vacate. The lease contains an automatic renewal clause. (1 year renewal)
No forwarding address was given.
The tenant claims a written notice was given with the last rent payment. The tenant to have been confused on the end date of the lease.

What are my options?
Do I just keep the security deposit?
Should i sue for the full year's rent...plus the last month on the current lease?

I'd greatLY appreciate any and all responses/opinions

Thanks

Bob