Calicut University — Non availment of challan receipt

Sir,
I have been registered for b com 4th semester examination yesterday. However i was unable to download the challan receipt. My bank account had been debited as soon as i made the payment. Also i had received the challan number and security code for the purpose of registration. The issue i am facing now is the server shows invalid while i am trying to download the challan receipt, even after giving the correct challan number that i had received by way of SMS.