Service tax refund querry

hello to all, I need help regarding refund issue of service tax there was output tax liability to be paid by me in first half of FY-15-16 which i settled through cenvat credit (input credit) but by mistake i also made the payment of output tax liability also and the same challan has not been shown by me in service tax return of first half and nor in the service tax return of second half of FY-15-16 so please help me by suggesting how can i take refund of excess amount paid