Found an employee on the Exclusions list OIG - what now?

I have an urgent situation. We have just completed our monthly compliance check and have discovered that one of our medical billing contractors is located on the OIG Exclusions list. This contractor was hired 6 months ago and passed the initial background verification without any issues whatsoever. I am panicking now that I know that this may be very serious for our clinic and may put us in jeopardy of incurring stiff penalties. What is the next step? Should we terminate this contractor immediately? Also, will we need to self-report to CMS about this? Please provide me with assistance!