I agree with Justin.
Your notice due by 3/16/2010 is only your stated intent under terms of your lease to vacate within 30-days. So you have promised to vacate by 4/16/10. But that only serves your notice requirement, not your final action. That notice is to give them time to re-rent. A courtesy to them. It does not directly address your financial obligation.
When your rent becomes due on 4/1/2010, you are still a resident, and thus are obligated to pay a full month, but are permitted to move out as of 4/16/10 without penalty, and apparently with return of your security deposit.
But you have paid all of April rent. How that will be handled in any reimbursement to you for the period from April 16th until April 30th should be covered under another term of your rental agreement. What does your lease say about reimbursement of any pre-paid rent after vacancy of the property? This is separate from your release from future obligations under the rental agreement.
In the worst case, this is how I see it. You deliver a 30-day notice by 3/16/2010.
YOu must must pay a full month's rent on 4/1/2010.
Then the financial department takes over. You want, and are probably entiled to, a return of your full secutity depost.
But that is only a part of their final financicial settlement with you, which will be offered as one package, and maybe months from now. If you contest pro-ration and return to you of rent that you paid for the period of April 16-30th, after you moved out, that will go to their legal department for review of the terms of your lease.
It may be months before they settle with themselves, and with you.
I would not expect any prompt return of security deposit or any requested proration of unnoccupied rent.
