HELP - cheque for invoice already paid

SOLVED

Hi,

I work for an Environmental Lab and we do work for different Consulting companies in the Oil and Gas Industries.  One of our consultants sent us work for an Insurance claim (oil spill) and paid us by cheque which I have deposited a while back.

Today I received a cheque for the same project from the Insurance company.

I contacted the Consultant and they requested that I deposit the cheque and then Issue them a cheque for the same amount.  I know this is doable but my brain is blank on the best way to do it so it doesn't affect the wrong accounts.

Does anyone have an idea?

Thanks,

LaChapa