Landlord deducting more money from the deposit.

Landlord deducting more money from the deposit. We have a rental agreement, which states we have to give one month notice. Since our landlord was kind all the days, we requested him, after we vacate, if none of new tenants turn up we will bear, one more month rent or else to consider prorated rent. We were paying rent on every month 5th. We had given oral notice for landlord on June 18th 2016. We had vacated house on June 29th 2016. While leaving the house, we had informed the landlord until July 5th we will pay the rent amount and until new tenant turn up, we will bear the prorated rent. Landlord didn’t made an issue at that time. By July 7th 2016, Landlord informs via WhatsApp as still new tenant had not turned up, so landlord will wait for one more week and do the final settlement. On July 17th 2016, Landlord turns up with break up , mentioning need to pay until August 5th (that’s an extra month rent) stating tenants will occupy home by July 25th 2016. When we requested landlord on call, he started stating you have not returned key in fomal way and few other words. Finally we went to house and cross checked on July 24th, new tenants had already occupied house from July 14th 2016. We have got phone number of new tenants. Now when we call our landlord , he states whatever he is doing is legal as we had not given him 1 month notice and every time we call him for discussion he states he has to take his kid to doctor or he has to consult his father-in-law. Is there any law we can claim, only proof I have about owner denying or asking one more month extra rent is WhatsApp messages. What we wanted claim is, Owner is claiming extra one more rent after we left, before that he didn’t spoke any word on that. Since owner is not in loss in any case, as we are paying one month rent as maintenance. We had an issue , as he is claiming extra month rent as notice period not given for 1 month. Its like, he is getting rent from new tenant and he got deposit from new tenants and he is asking rent for same month from us also. Is there a way, he has to declare that in income tax. How these things goes on? We just believed him, as he was behaving in decent way and he is working software professional.