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.
To help you with this issue, may I ask:
1) The FULL Model Number of the phone system you are working with? If this is a cordless system, that model should be printed on a sticker on the bottom or back of the MAIN base.
2) Can you please explain what "the NEW one" and "the OLD one" means? For example, did you just ADD an extra handset to the system?
3) Have the batteries EVER been replaced in these handsets? And if so, WHEN did this last happen?
Please REPLY using the box below.