Hello & Welcome,
Sorry 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 unit and START with KX-TG, but not have an "A" (which is just for the handsets).
2) How many TOTAL cordless handsets do you have with this system?
3) WHERE was this system purchased?
4) Are ALL the handsets part of the original system, or were there EXTRA handsets purchased separately?