The server to the official website has slowed down. With the last date being extended to December 26th, Candidates might be applying and hence the traffic to the website must have been more causing the website to slow down. Now please check if the payment has been debited from your bank account. If yes, wait for atleast until the end  of the day to check if it would be credited to your application. Or else, you have to make another payment and the first payment will be refunded to your account. If the payment has not been debited from your account, please make another payment.