Att SIM card got blocked?

So my husband bought a phone from ATT for me with service. I wanted an upgrade to the next size and so we went to a good used phone store and he bought me a used clean phone. It's been about 2 months but today my service has suddenly got cut. My daughter opened my iPhone sim slot and she noticed a black sim card also which means it's meant to unlock for any carrier. Just discovered it is a sprint phone so we figured I can just put my att SIM card back into my original iPhone but not the sim is just locked. Is there any way I can to to my local att store and just get a replacement SIM? If so can I go while my husband is at work or do I have to wait for him?

Instead of asking here,
you should have called your service provider
and asked the same questions.