Deposit deducted in absence of rental agreement

Hi Lawyers, Myself and my roommate used to stay in a apartment since April 2022 with 5000 rent and 10k deposit divided among us, but we didn't make any rental agreement neither our owner bothered about it. After one year the rent was increased to 5500 and we had no objection we continued to pay it. In December 2023 the owner called me up and asked to vacate the room as she wanted to sell the property urgently. I told her we will vacate the room as soon as I find one and she agreed to pay deposit amount whenever we vacate the room. My friend moved out on 28th Feb 2024 and asked me to take deposit from the owner and then we will take our part once I move out. I informed owner on 7th March that I will vacate the property on 10th March. She agreed to deduct the deposit on prorata basis. Once I vacate the property she made me wait one month by giving excuses to not give the deposit amount and then later she paid me only 4k stating . She has deducted whole month's rent as I moved out in middle of the month..now I don't have any of this thing documented. But I have all the proof of rent I paid online and deposit that I paid to her.Can I get any help to recover the full security deposit?