We had similar problems until we got Call Guardian. It is excellent, I am not trying to sell it to you just a suggestion. We now find that if a telephone number is not in our phone, it has to go through to the operator, they in turn ask the caller to give their name and telephone number the operator then gives us three choices, either to press 1 to be connected, two to refuse and three to go to answering machine.
Thanks Mamya, that was reassuring so I called and retrieved. It was a friend texting landline by mistake. I forgive her! Never quite sure with these unknown numbers and messages.
Thankfully we don't have too many unwanted calls Guillie. We have registered with TPS and have caller display. If we don't recognise the caller we let it go to answer machine, then see what happens from there. Can always pick up once if they start to leave a message.