House owner not taken the house key and also not giving security deposit

The house owner brotherinlaw is in airforce named Sudhakar. Sudhakar is the one who spoke to us while giving the house stating house owner is abroad and he is caretaker. He took 6 months of rent as security deposit which is 1.5 lakhs. Even after mutually agreeing date of vacation, he has not come on day of vacation. Instead he asking us to hand over key to third person. When asked about security deposit, he says he will come later and do inspection and return our advance. My questions: 1) As the key is still with me, do I have to pay him rent?? It's him who has not come till now... Last month he sent legal notice demanding that rent has not been paid till date and the notice is to pay rent till date and mental torture etc to give him more money. 2) what should I do with the house key?? Incase if I have to pay rent as long as I have key with me...actually the house in one state and the person lives in the other state of India. 3) the agreement is not registered as per new rule in tamilnadu. Does the agreement still hold valid?? 4) how will I get my security deposit..I paid rent till date of vacation as intimated on time... 5) he used abusive words in whatsapp...I filed a police complaint...he abused me as bitch and my son born to my neighbour... Does whatsapp messages hold as evidence?? Iam a woman and he lately calls only late-night disturbing my sleep and my husband sleep. Police filed this complaint as CSR and Not FIR...what should I do with this complaint?? He asked police a week time to appear physically but till date no news what's happening with the case. 6) please note I gave my replies to the legal notice he sent...I sent reply to his lawyer through his whatsapp... 7) please let me know if this situation is in my favour?? I don't like to visit police station or court...but he insists only through court and he says that he is in upper hand and he will definitely win the case... Does this situation is in my favour or not??