Landlord postponed move-in by 10 days...?

I live in California. My 1-year lease is up on September 30th. One year ago when I moved in, my landlord agreed (and I have in writing) that my move-in date was August 31st, 2008. However, after I rented the U-haul and had my things packed up the day before, I got a call stating that the unit wasn't ready and that they were postponing the move-in date. I had signed an agreement stating I was getting a FULL month of rent free (and they signed a one-time concession of the rental amount of $625). I ended up not being able to move in until September 10th, which means I had a full 11 days of essentially "free" rent wasted. Now that I am moving out, can I request a credit for those 11 days they stiffed me? Do I have any credence due to the signed doent that produced a move-in date (and takeover of financial burden) on August 31, not September 10th? I am very upset with this landlord for various reasons, including the requirement to vacate my apartment 5 times during the year for "pest control" that essentially did nothing (there is still an infestation of roaches) as well as them ignoring several maintenance requests, including a request during the dead of winter that my hot water heater was out. I took FREEZING showers for one week before I marched in and complained again. They are trying to charge me fees for various things, like the fact that during one of the pest spraying, they came the day AFTER they told me that I had to have the unit ready for them. I ended up having to box ALL of my items up that I'd just put back and now they're claiming I have to pay fees for their "time". Its just...irritating. I figure if they're going to charge me these fees, then I am going to at least try to get my credit for the 11 days they made me wait for my unit, that I'd put a deposit on August 8th, 2008.