My late father's phone started receiving good morning my love

My dad died in March. We left his line on for bank alerts. Since then a message comes in most mornings around 6, good morning my love, from a number he saved as Plumber 2. I told myself it could be a wrong number or one of those broadcast things. Yesterday the person wrote that he has been quiet and asked if she should come to the house. So it's somebody who knows the house. Mum hasn't seen anything. I don't know if I'm protecting her or just scared.