Student or Learner
Is this incorrect in written English?
Is anybody there?
Someone told me, anybody is only used in spoken English and not used in written English?
Is it true?
They are both correct. I've never even heard of any such rule.
And neither has
The Cambridge Guide to English Usage
• The book is based on extensive, up-to-date corpus data rather than on the author’s personal intuition or prejudice
• It is truly international in scope, differentiating clearly between US, UK, Canadian and Australian
usages and referring to other regional varieties as required
• It is clearly and accessibly written, for easy use by anybody concerned with accurate communication in English, whether as a student, a writer, or in other business and professional spheres
(from their own introduction to their own book)
The Cambridge Guide to English Usage - Cambridge University Press
Maybe someone cheeky was pointing out that when, in the dark, you're asking if you're alone, you don't send a letter or pass a note. You call out loud.... Could that have been the meaning of the 'someone' who said so?