How to re-activate my AT&T SIM card?

Alright so I got a Iphone 4s from my mom and the SIM card is deactivated since she stopped using it. How can I reactivate it? I went to AT&T site and tried activating the phone and it said my SIM card number did not exist and I found out that means it's deactivated. I need it tomorrow for a lot of things. And I can't call them because their hours don't go this late. Need a answer As soon as possible please thanks

The best thing to do (if you have access to another phone) is to call AT&T on this one. They should be able to look up the sim card details if you can provide them the numbers on the sim card. Once they have this, they can tell you whether they can reactivate it or if you need to go in to an AT&T store to get a new micro sim card.