Deposit money

My son had rented a house at andheri west on 10th February 2015. he, due to certain reasons wanted to vacate the house by mid May 2015. i had talked to the landlady and informed her about this around via Whatsapp messaging and she confirming 21st April 2015 will be taken as the notice date. Then latter she asked that my son should give a written notice which my son handed over to their broker staying next door on 25th April 2015 but dated 24th April 2015. Upon informing the owners that he has handed over the letter to their broker, they said that it should be handed over to them and not some third person I informed them that the letter has been handed over to Mr. Nigam, the Landlady said that it should be handed over to them and not to any third person. So, my son handed over the letter to them personally on 28th April 2015. He left their house on 15th May 2015 and left the keys with the their broker. The issue now is that they are deducting their registration money of Rs. 3000/- and extra one month rent