SqlDataAdapter not updating rows in Database

I am using SqlDataAdapter to update my dataTable which I had queried from Database in another method and in that method there were columns, Status and Is_processed which were updated.
Now, I want these changes to be persisted (updated) in Database. Following is what have done to achieve:

Code

 batchSize = 10;

string cmd;

    int updatedRows;
    try
    {
        string connString = db.ConnectionString;
        using (SqlConnection conn = new SqlConnection(connString))
        using (SqlDataAdapter adapter = new SqlDataAdapter())
        {
            cmd = "UPDATE IMPORTED_ACCOUNTS SET STATUS = @Status , IS_PROCESSED = @IsProcessed " +
                   ", CREATED_ON = @CreatedOn , CREATED_BY = @CreatedBy , UPDATED_ON = @UpdatedOn , UPDATED_BY = @UpdatedBy " +


 "WHERE CONVENTIONAL_ACCOUNT = @ConAcct";
        adapter.UpdateCommand = new SqlCommand(cmd, conn);
        adapter.UpdateCommand.UpdatedRowSource = UpdateRowSource.OutputParameters;
        adapter.UpdateCommand.Parameters.AddWithValue("@Status", "Status");
        adapter.UpdateCommand.Parameters.Add("@IsProcessed", SqlDbType.Bit, 1, dTable.Columns["IsProcessed"].ColumnName);
        adapter.UpdateCommand.Parameters.Add("@CreatedOn",SqlDbType.DateTime,30, dTable.Columns["CreatedOn"].ColumnName);
        adapter.UpdateCommand.Parameters.AddWithValue("@CreatedBy", dTable.Columns["CreatedBy"].ColumnName);
        adapter.UpdateCommand.Parameters.Add("@UpdatedOn",SqlDbType.DateTime,30, dTable.Columns["UpdatedOn"].ColumnName);
        adapter.UpdateCommand.Parameters.AddWithValue("@UpdatedBy", dTable.Columns["UpdatedBy"].ColumnName);
        adapter.UpdateCommand.Parameters.AddWithValue("@ConAcct", dTable.Columns["ConventionalAccount"].ColumnName);

        cmd = "INSERT INTO IMPORTED_ACCOUNTS ([STATUS],[IS_PROCESSED],[CREATED_ON],[CREATED_BY],[UPDATED_ON],[UPDATED_BY], CONVENTIONAL_ACCOUNT) " +
              "VALUES (@Status , @IsProcessed, @CreatedOn, @CreatedBy, @UpdatedOn, @UpdatedBy, @ConAcct) ";
        adapter.InsertCommand = new SqlCommand(cmd, conn);
        adapter.InsertCommand.UpdatedRowSource = UpdateRowSource.OutputParameters;
        adapter.InsertCommand.Parameters.AddWithValue("@Status", dTable.Columns["Status"].ColumnName);
        adapter.InsertCommand.Parameters.Add("@IsProcessed", SqlDbType.Bit, 1, dTable.Columns["IsProcessed"].ColumnName);
        adapter.InsertCommand.Parameters.Add("@CreatedOn", SqlDbType.DateTime, 30, dTable.Columns["CreatedOn"].ColumnName);
        adapter.InsertCommand.Parameters.AddWithValue("@CreatedBy", dTable.Columns["CreatedBy"].ColumnName);
        adapter.InsertCommand.Parameters.Add("@UpdatedOn", SqlDbType.DateTime, 30, dTable.Columns["UpdatedOn"].ColumnName);
        adapter.InsertCommand.Parameters.AddWithValue("@UpdatedBy", dTable.Columns["UpdatedBy"].ColumnName);
        adapter.InsertCommand.Parameters.Add("@ConAcct", SqlDbType.VarChar, 100, dTable.Columns["ConventionalAccount"].ColumnName);

        cmd = "DELETE FROM IMPORTED_ACCOUNTS WHERE CONVENTIONAL_ACCOUNT = @ConAcct";
        adapter.DeleteCommand = new SqlCommand(cmd, conn);
        adapter.DeleteCommand.UpdatedRowSource = UpdateRowSource.OutputParameters;
        adapter.DeleteCommand.Parameters.AddWithValue("@ConAcct", dTable.Columns["ConventionalAccount"].ColumnName);
        adapter.UpdateBatchSize = batchSize;
        updatedRows = adapter.Update(dTable);  // point where code breaks
    }
    return updatedRows;
}
catch (Exception ex)
{
    return 0;
}

Error

It ends up with the following error in catch block:

Violation of PRIMARY KEY constraint 'PK_ACCTS'. Cannot insert duplicate key in object 'dbo.IMPORTED_ACCOUNTS'.

Comment Why is it trying to insert rows in database when they should be updated as they already exists in the Database? What are the conditions for adapter.Update(dTable) method, when it triggers Update rather Insert?

Can't figure out... Help is indeed appreciated!