Stolen Checks = Late Rent

I hope they don't charge you a late fee.

Once you dropped the check in the designated drop box, it's their check as you've relinquished control of it. If they tell you there is a late fee, I'd counter with this.

Good luck and those situation always suck. the other bad part is not only can they wash the checks of original payees, they also have all the info to make a fake set of checks.