1) you ought to have entered into registered leave and licence agreement before taking premises on rent
2) since there is no written agreement licensor cannot make additional deductions on account of your vacating premises earlier .
3) in the event licensor is asking for 3 months time to return security deposit ask him to give post dated cheque for security deposit amount
4) also ask licensor to give in writing that said cheque is towards refund of security deposit lying with him for taking premises on rent .
5) if licensor refuses to give in writing dont vacate the premises till entire security deposit id adjusted