Calcutta Electric Supply Corporation [CESC] — Get back the extra money paid by me during lockdown period

I Shri Stabak Mitra. My Customer ID [protected]. I have already paid the bill of may 2020 during lockdown period but now in current month august 2021bill, I came to know that bill kept in abyance was being added in consecutive 10 installment. And without being aware of the paid amount I have paid these 10 installment also kindly go through the matter and help me to get back the extra money paid by me.