Confusion and anger are common emotions expressed by someone with Alzheimer’s when you try to explain that someone is deceased.
Do not argue with them. One suggestion is to simply “go” with the delusion. You may even dial the phone and tell them that the deceased person isn’t home right now.
Try talking to them about what they love about the person they don’t understand is no longer living.
Don’t try to “straighten them out.” Go with what is upsetting them, try to provide some comfort and stay calm. Distract them when possible.