Landlord not returing the security deposit

I was renting a flat for 4 yrs but now as the flat was too old and owner not ready to repair the interior and also he was increasing 10 percentage on every yrs renewable I thought to vacate the flat, the leave and licence agreement was expired on dec 8th and in jan 17 I called him over phone but he did not responded. The owner is in USA and he has a POA given to his friend and called both them but they did not picked my call on 17 of jan so I whatapp them saying that the flat would be vacated on or before 7th feb but I vacated the flat on 31jan itself and send him an email that the flat is vacated and return the deposit and take over the keys. but now they have return back to me saying that they will deduct 2 month rent as I have not given them written notice and they say whatapp msg is not legal. the I had informed him to deduct the jan rent from the deposit and return back the balance amount but they are just over msg reply and stick to deduction of 2 month rent and they will recover also deduct the damage if any in the flat. I had already informed him regarding the wear and tear of the flat and slo I have all the voice calls recorded on all this conversation. the building society has informed not to hand over the keys unit the deposit is clear or else you will not get your deposit. as I said the agreement is already expired in dec but due to dispute in increasing rent and flat condition I thought to vacate it and I was feeling that the owner and the POA is not responsible guys and never do what is required in the flat maintenance . even couple of times I was told to pay the outstanding maintenance bill and property tax deduct it from the rent amount but for this I have already taken official email from them before I transfer the amount towards paying of the bill and the agreement clearly states that tax and maintenance should be paid by Landlord. he has given me date over email on 13feb to come and have a look at the flat and settle the balance amount but not sure how much I will get back as he tells me that since no written notice is given he will recover 2 month rent. I went to local police station but they told that it civil court case so they can just call the POA and try to resolve it but still no change in their words. let me know what I should do next