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Hello & Welcome to Just Answer,
I'm Greg and will do my best to assist you today.
Sorry I didn't see your question earlier and to hear of any issue you are having with your phones.
I believe what you are describing is the "key lock" feature of these handsets.
I have the description of this feature AND the steps needed to turn this feature ON and OFF. See attached image.
NOTE: You MAY have to click on the image name to see the image.
Please give these steps a try and let me know if that unlocks the handset.