SIM CARD DISCREPANCIES

I bought a replacement phone for my ATT prepaid account, the previous phone screen broke and so I needed another. When I placed my current, active SIM card into the new phone, the SIM status displayed that the card and service was active, but there was an X through the service indicator. I called ATT and a recorded line informed me there was a problem during activation and that I needed to bring it back to the retailer in order for them to activate the phone. I did this and ended up exchanging the phone with a new one of the exact same model, and found myself facing the same issue. I used my wife's active SIM card in the new phone, in place of mine, and the service worked fine. When I placed my (original, working) SIM card into her working phone I got the same error as before. So obviously the problem isn't the activation with the retailer rather it's present within the SIM card itself but I don't know what exactly it might be.