How to sue for unnecessary deduction of Security Deposit

My wife rented a house in Bangalore last year in the month of April 2016. April 2017 we decided to vacate giving 1 month notice which the landlord agreed. While discussing about the Security Deposit refund they quoted more than a month rent for painting than what mentioned in rent agreement which we duly questioned. Now they are deducting more amount than what they asked earlier stating that we should have given them 45 days notice. It all started when we questioned them for the unnecessary deduction. They gave a new quotation which has unnecessary deduction and when questioned again they intentionally delayed the refund by 1 month. I contacted them on my wife's behalf then they started demanding our marriage certificate which is irrelevant to this case. They are harassing us mentally by putting new clauses every now and then. Please suggest what to do in this situation.