Phone call from strange number?

I'm in California, and don't know anyone from Oklahoma, but I received a ring from there. I did not answer, but when I tried calling put money on, the number was invalid. Any thoughts?

Free VOIP requires phone number-I don't enjoy one?

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Answers:    I'm base in UK (you've submitted this on UK & Ireland ceqna.com)

but I usually google unknown numbers and you find they are someone trying to get rid of you something, or someone else has already found out who is trying to contact you.
I would never telephone call them back as within Uk we have plentiful expensive scams.

Good luck

Why do peoples' voice nouns different when they're chitchat on the phone?

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Could be a wrong number, charity organization are exempt from the do-not-call list so that could be it, or a collections agency...