Hello & Welcome to Just Answer,
Sorry to hear of any issue you are having with your phones.
To help you with this issue, may I ask:
1) The Make & 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.
2) What phone service provider (phone company) you have for this phone line?
3) Can you do a quick TEST for me?
That TEST is to pick up any handset in the system and QUICKLY listen for the dial tone. Please let me know if you hear ANYTHING unusual BEFORE the CLEAR dial tone, such as any "beeps" or "pulsed" dial tones.