weired problems

I want to extract invoices whose status is open and whose duedate is between a certain time and today. I have wrote the scripts as follows:

var searchFilters = new Array();
  var searchColumns = new Array();
 
  searchFilters[0] = new nlobjSearchFilter( 'duedate', null, 'after', 'daysago15' );
// searchFilters[1] = new nlobjSearchFilter( 'status', null, 'anyof', 'open' );
 
 
  searchColumns[0] = new nlobjSearchColumn( 'entity' );
  searchColumns[1] = new nlobjSearchColumn( 'email' );
  searchColumns[2] = new nlobjSearchColumn( 'total' );
  searchColumns[3] = new nlobjSearchColumn( 'status' );
  searchColumns[4] = new nlobjSearchColumn( 'trandate' );
  searchColumns[5] = new nlobjSearchColumn( 'duedate' );
 
  var searchresults = nlapiSearchRecord( 'invoice', null, searchFilters, searchColumns );
 
I have two problems: one is that why this search is returning duplicated records. the other is how could I only select the ones with the status open. From the guide I could see that the record field status is text type, however the search column and search filter for this is select. there are multiple operators to select type. which should I use?