Liability on Security Deposit Contract Mistake by Prop Manager?

[David Slattery]

Hello, I can't find info online about this situation, so thought I'd pose the question here...

Short story: I'm the property owner and have a tenant leaving this month at the lease termination. Security deposit collected a couple years ago was $600 and that was stated on the original lease's Security Deposit addendum. The contract for the current year's lease mistakenly says $1200. Am I liable for the correct $600, or does the signed contract make me liable for $1200?

Longer story context: I had a very shady property manager who made TONS of mistakes and negligence. I left at the end of last year and have just settled all of their other mistakes with them, but this is the last one. They insist that the law protects from mistakes, so $600 is all that I would be liable for (and all that they want to return to me as the tenant's security deposit). However, I demanded the $1200 that their signed contract with them (on my behalf) and the tenant states. Am I right to expect $1200 from them, or are they right that the law protects property managers from mistakes like that?