The message "Do you want to call using your remaining line?" appears on phone with Dual SIM when the system detects the line you tried to use for a previous call is no longer active, and it's asking if you want to use your other active line instead.
The reason is that your have not removed your old sim card from your previous provider yet. If the old one is a physical sim, remove it, if the old one is an eSIM, disable it. After you have done that, Reset network settings on your phone
