Tamil Nadu Electricity Board [TNEB] — payment gateway not working

Address:

KARAPAKKAM, Chennai, Tamil Nadu, 600119

The due date for my cc bill for bimonthly bill was 4 march. I tried to pay the bill through website but the payment link was not working throughout 1 week.
After the due date it's working absolutely fine.
I have been charged late fee which is unjustified, since the site is not responding even 1 week before.
I have exceeded the due date, but now the option for paying only the cc is not coming