Dear Nisha, AIIMS hss closed its final registration process on March 12th including the option of making a payment. Now you cannot complete the registration process as the last date has been closed and AIIMS hasn't released any notification regarding an extension. If you are interested in pursuing medicine, please fill in the JIPMER application form. 

Hii

IF there was error with the payment, you were supposed to make the payment again. Incase of double payment, 1 amount would have been refunded.
But now as the last date of registration is over and the registration has been closed, there is no chance of making the payment now.
No notice of date extension has yet been put up on the website. IF there wouls be any date extension, you will get informed through the website itself. But as of now, you can not make the payment and need to wait for next year chance.

Thanks!