Notice period for vacating a rented property - misinterpreted

Hi community, I live in a rented apartment in Bangalore and am planning to vacate it. I tried calling the point of contact for informing him of the same but his phone number was invalid, after a few days I wrote to him and finally gave him notice of 30 days on 20th April absorbing the loss of the few days I was unable to reach the person. However to my surprise the owner's representative are saying that the notice is as per a calendar month and not 30 days. They are adamant that I will have to stay in the house till May end and not till 20th May. They are behaving very rudely and asking me how they will get a tenant in the middle of the month when I myself moved into the flat on 10th of the calendar month. The owner is a builder and owns a lot of flats and his entire team is rude and unprofessional (cunningly only after the agreement is signed). I am yet to vacate the house and recover my deposit but looking at this I have a feeling I will be cheated out of a lot of my due. What should I do? Best, Ojas