This is in the state of Hawaii.
I recently moved and checked out of my prior residence. I gave 28 days notice on the 17th of April. I know by my contract and by state law that I must pay any portion of a month within that period. By that law I am required to pay 15 days of rent. I had told my landlord that I would be ready to vacate on the 1st of May. On that day they did their inspection, which I signed, followed by the check out form. There was no mention of the 15 days of rent owed.
Today I received in the mail a notice that per the prior agreement I owed 15 days of rent. My question is if the contract is still valid or was it terminated when I and the landlord signed the check out document?
One further question is how am I able to determine if the landlord has been dragging their feet about re-renting the unit? I have a friend in the building and they've informed me that the land lord spent 2 days working on the unit and has since done no more work. The unit has not been advertised on any classified or website listing so far as well. Thank you for your time.

