Hello & Welcome to Just Answer,
Sorry I didn't see your question earlier and to hear of the issue you are having with your phones.
May I ask:
1) The Make & Model Number of the phone system you are working with?
2) WHEN did this issue first begin?
3) What phone service provider (phone company) you have for this phone line?
4) If you have ANY other devices (phones, fax, alarm system, etc.) attached to this same phone line (not part of the cordless system)?
I ask all these questions to see if this is a "phone issue" (not as likely) or a "phone service issue" (more likely).
To get to the bottom of this, the first thing I usually do is disconnect ALL devices - from ALL phone jacks - to isolate any issues with ANY devices that may be causing this issue.
And WHILE EVERYTHING has been disconnected for AT LEAST FIVE MINUTES (and still disconnect), I place a TEST CALL to the phone number where these devices were connected (from an outside line - like a cell phone or neighbor's phone).
If I hear a "busy signal" OR the TEST CALL goes immediately to a "Voice Mail" system, then that points to an issue with the phone SERVICE (being stuck ON), and it would be time to contact the phone service provider - to report the problem and have it looked into.
BUT, if the TEST CALL goes through, and I hear multiple rings, then I will reconnect ONE DEVICE at a time - and check for a dial tone on the phone line, and that the "line in use" has gone away.
I will then continue to TEST by placing an OUTGOING TEST CALL, to make sure that works.
If it DOES work, then I will continue to add other devices (that were connected before), and TESTING after each device is added, until I either have all devices attached (and working) OR one of the devices causes the line to hang - in a busy state (and the line in use comes back).
That it the basic troubleshooting process that I would use in this case - to find where the real issue is. Once found, the appropriate action needs to be taken (Contact the provider if a phone SERVICE issue, or disconnect the offending device, if found to be a device that WAS connected previously).
I hope this helps. Please let me know what is found or if you have more questions.
Thanks, ***** *****
P.S. I will be offline for a while (its getting late here), but should be back on in 8-9 hours, if you have further issues or questions.