Delhi University — Examination fee paid but slc portal still show to pay it

I have paid my examination fee INR 510 for second semester ug exam the amount got deducted from my bank account I wait for the payment approval in portal for 5 minutes as well but slc portal again shows to pay the fee.
Please refund my 510 rs which got deducted from the account.
I tried to contact du officials through mail soo many times didn't get any reply please resolve it.