Conference organizer pushes to Journal instead of Conference Proceedings Recently  a paper was submitted to ICIMP 2018(will be held at Imperial College London - South Kensington Campus,  London, UK during  Jan. 12-14, 2018 .).
Organizer  told that the  paper is accepted for publication in JOIG and ' Welcome to participate in ICIMP2018'.
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But it is written on the webpage of ICIMP 2018 that-


  All the accepted papers of ICIMP 2018 will be included into Conference
  Proceedings which will be published by IEEE. And they will be archived
  into IEEE Xplore and be indexed by EI Compendex and Scopus.


If the paper is accepted for the conference then why it will not be published in
Conference Proceedings which will be published by IEEE? Why do they push it to a journal ? Is there a convention like what I stated above? Is it ok/legal to switch like that? 

PS: The incident didn't happen to me, I was informed the incident by a forum member, I suspected/suspect, the paper author is lying about the acceptance, it is highly unlikely that such thing can happen.
Publishing peer-reviewed conference proceedings in an associated journal is a trend gaining traction in CS lately. Many universities are pushing quantitative evaluation of researcher output and punishing conference-as-publication fields, so this is to help researchers make the case for their productivity to the layers of administration that aren't familiar with the venues of a given field.

But your case sounds odd, especially since you weren't told beforehand, and the journal doesn't seem to be affiliated with IEEE at all. Definitely contact the organizers and make sure this isn't some scammer pretending to be them to snipe the paper out from under them...

If they really have chosen to change the publication venue, you don't have to accept it: you can always decide to withdraw your paper instead and submit it elsewhere.