That is not supposed to happen. I would call ATT customer service and report it.
the Carrier code that is broadcasting from that tower should be showing ATT, but for some reason it is still broadcasting the Centennial Carrier Code. This is how one carrier can roam on another carrier and still appear as if you are on your home carrier.
I've seen it happen a few times with different company names. It usually happens when I'm in the middle of nowhere but I suspect it has to do with what is going on with the network in a specific area.
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