I don’t know how POTS works in other countries, but around here the call ends only when the caller puts the handset back to its cradle. If the callee hangs the phone, he can pick it up later (assuming the caller hasnt hanged up in the meantime) and resume talking.
So if the caller for whatever reason doesn’t hang up, callee’s line will be engaged the whole time.
Is there anything the callee can do to cancel the call?