Getting ctd reference no.

sir, I regularly pay tax online,but this month while paying VAT online due to lapse of screen I couldn't trace the CTD reference no. which is must for filing VAT monthly returns.even I went to commercial taxes site and chose print challan option wherein I have to put RC no. date and amount of tax paid but still I get the message as invalid transaction.even enquired the bank but they are not able to trace the CTD ref. no.how can I get the CTD ref. no..please help