Hi smile,
You need to add another condition in the where clause for filter the record. The condition should be get the AdmissionNo from tblFeesCollection where the month is 11-Nov and Paid greater than 0 and pass AdmissionNo to not in condition.
Check the below test query.
SQL
DECLARE @tblFeesGenerate AS TABLE (AdmissionNo VARCHAR(10),Month VARCHAR(10),Total INT)
INSERT INTO @tblFeesGenerate VALUES('R-02','10-Oct',500)
INSERT INTO @tblFeesGenerate VALUES('R-03','10-Oct',500)
INSERT INTO @tblFeesGenerate VALUES('R-04','10-Oct',500)
INSERT INTO @tblFeesGenerate VALUES('R-02','11-Nov',500)
INSERT INTO @tblFeesGenerate VALUES('R-03','11-Nov',500)
INSERT INTO @tblFeesGenerate VALUES('R-04','11-Nov',500)
INSERT INTO @tblFeesGenerate VALUES('R-05','11-Nov',500)
INSERT INTO @tblFeesGenerate VALUES('R-06','11-Nov',500)
INSERT INTO @tblFeesGenerate VALUES('R-07','11-Nov',500)
					
DECLARE @tblFeesCollection AS TABLE(AdmissionNo VARCHAR(10),Month VARCHAR(10),Recievable INT,Arrears INT,NetBal INT,Paid INT,RemBal INT,CollectionDate VARCHAR(10))
INSERT INTO @tblFeesCollection VALUES('R-02','10-Oct',500,250,250,200,50,'10.10.18')
INSERT INTO @tblFeesCollection VALUES('R-03','10-Oct',500,0,500,300,200,'10.10.18')
INSERT INTO @tblFeesCollection VALUES('R-04','10-Oct',500,0,500,0,500,'10.10.18')
INSERT INTO @tblFeesCollection VALUES('R-04','11-Nov',500,500,100,700,300,'08.11.18')
select fg.AdmissionNo,sum(Total) 'Recievable',RemBal 'Arrears', isnull((sum(Total)),0) + isnull((RemBal),0) 'NetBal',fg.Month
from @tblFeesGenerate as fg 
left join @tblFeesCollection as fc on fg.AdmissionNo=fc.AdmissionNo 
where 
fc.AdmissionNo is null or fc.AdmissionNo is not null and
fg.Month='11-Nov' and
fc.AdmissionNo NOT IN(SELECT AdmissionNo FROM @tblFeesCollection WHERE Month = '11-Nov' AND Paid > 0)
Group by fg.AdmissionNo,fg.Month,RemBal 
order by AdmissionNo
Output
| AdmissionNo | Recievable | Arrears | NetBal | Month | 
| R-02 | 500 | 50 | 550 | 11-Nov | 
| R-03 | 500 | 200 | 700 | 11-Nov | 
| R-05 | 500 | NULL | 500 | 11-Nov | 
| R-06 | 500 | NULL | 500 | 11-Nov | 
| R-07 | 500 | NULL | 500 | 11-Nov |