Have you confirmed that the issue is with the instrument and not with your provider?
With your landline provider first confirm that there’s no line or any other fault with the landline connection. If the issue persists beyond your instrument, then using another device may not help. Try to get another instrument from your friend or relatives and confirm that your device indeed is faulty.
Personally, I am using Panasonic kx-tg3611sx for last few years. No issues so far.
*www.panasonic.com/in/business/phones-communication/phones/cordless-phone/kx-tg3611sx.html