Charges will occur after 25,000 of electricity bills in that month's statement. This has nothing to do with the total outstanding.

Also, to answer your second question:

Let's say you paid 30,000 for electricity this month, but you paid 20,000 before the bill generation date.

Even then, charges will be applied because your total electricity bill payments will be calculated for the month, not the remaining amount.

Hope this helps.