How to renew over the phone

I have had a prepaid ATT card for over 10 years.  Same card.  I always added minutes over the phone.  I do  not have the actual physical card anymore.   I had the card so long i memorized all the numbers.   when i make a call now, there is no option to renew over the phone-- they tell me to go online where they will ask me for a pin # which  i do not know. How can i add minutes?