Thanks for posting your question.
As it appears from your query, there was no clause in the contract between you and the landlord which states about deduction of one month's rent in case the premises are vacated before 11 months. Hence, by doing so the landlord has breached the contract which existed between the both of you.
My suggestion regarding the course of action to be taken is as follows:
1. Send a legal notice to the landlord demanding the deducted rent and stating that in case of non-compliance the landlord must be ready to face appropriate legal proceedings.
2. Since the above transaction amounts to breach of contract, you may file a civil suit regarding the same. However, the amount involved is a small sum and the cost of contesting the suit itself might exceed the sum involved. Hence, I will suggest you against it.
3. You may file a criminal complaint/ F.I.R. under section 406 IPC for criminal breach of trust, stating that you had kept the deposit with the landlord as a security amount and now the landlord has misappropriated the money and despite specific demand is not repaying the same. Here, because of the threat of police/ criminal proceedings, the landlord might return the money. In strict sense, the offence under section 406 IPC is not made out, however, this is done to arm-twist the accused to reach a settlement.
From the above, to begin with, you must send a legal notice and many times it is sufficient to get the money recovered.
Do let me know in case you require any further clarification.