I just found out that part of the house I purchased 7 yrs. ago was built on a neighbor''s property. It is going into foreclouser now.What am I to do?

This depends on a number os things.  The first step is to review all of the surveys and determine exactly where the house is located relative to your neighbor's property.  And depending on how long your house has been there, and depending on the particular nature of the use of your neighbor's property, there may be certain laws that would grant you ownership in the part of your neighbor's property where your house sits.  A local attorney could easily determine if this might be an option in your case.