AZ - last month rent and security deposit

[Jack Stone]

We have a tenant who wants to use their security deposit as last months rent in Arizona. 

AZ law enables a security deposit to be a max of 1.5 months rent. Which we collected. Now that they are leaving they want to not pay rent and use the final month payment out of the security deposit for the last month. i don’t see anywhere in the lease or law that this is allowed. 

curious to get others opinion and if they don’t pay what are my next best steps.