Punjab State Power Corporation [PSPCL] — regarding online bill payment of electricity

My bill account no. Is g31kf420919m. On 01/08/2017, i have paid bill online but in next bill, previous amount was added. When i have checked online repicept it's showing in advance payment instead of bill paid please solve the problem. So that i can clear my over due bill as soon as possible.
Thanks in advance.
For any other detail call me on [protected].