How To get Missing Rows

Dear experts,

var result = (from p in excel2table.AsEnumerable()
                                      join v in LinkedBills.AsEnumerable()
                                      //This is how you join by multiple values
                                      on new { no = p.Field<string>("doc_no") }
                                      equals new { no = v.Field<string>("bill_no") }
                                      into jointData
                                      //This is how you actually turn the join into a left-join
                                      from jointRecord in jointData.DefaultIfEmpty()
                                      where jointData is null
                                      select new
                                      {
                                          doc_no = p.Field<string>("doc_no"),
                                          linkamt = jointRecord?.Field<decimal>("linkamt") ?? 0
                                      }).ToList();

above query giving me no rows, 

if i remove where joindata is null, i get all rows in excel2table and  unmatched rows has linkamt=0

this is too much of data which is not requied. the purpose of this query is to find missing doc_no and unmatched linkamt

but i want only doc_no not in linkedbills or excel2table.linkamt <>linkedbills .linkamt