Bank Req not balancing

We have an issue where our bank req is not balancing. The amount is
for the exact amount of a check we had an issue with. What happened
is they cut a check to the wrong Vendor in one period, then closed the
month. In the next month they Voided the check and then cut one for
the same amount to another Vendor. I am trying to figure out where to
look to see how this is affecting us. It looks like the GL
tranactions are all correct it just does not balance.