Is it normal to be afraid of strangers

Ever since I can remember adults have always been telling me to: "Don't talk to strangers!" Every day. Somebody somewhere told me to watch out for strangers. They still do. All the stories have really messed with my brain and now whenever I have to talk to somebody I don't know I freak out. People my age and younger are okay... easier to talk to that older people but still hard. I find it hard to order lunch from a cafe or anywhere. Anybody behind a counter freaks me out too. I think this is unreasonable but I want to know Is it normal? Does anyone else have this? I also am afraid of answering the phone, for fear that it's someone I don't know. Because the idea of talking to someone I don't know and can't see... again freaks me out. The phone is a more extreme case than the face to face talking. Before you ask, yes I do have friends, many. It's just that i find it hard to talk to anybody new. I think it is derived from the fact that every adult tells me to "Watch out for strangers." Also with the phone thing my fear is heightened possibly because I used to watch a load of scary movies and almost all of them ended with someone being killed after answering the phone to find the killer on the other end. Please, is this normal?