It is to ask that I sent my original article in some journal, reviewers asked me to make some amendments which I did on time. The editor then sent me an email with their decision of acceptance. Now they have published their journal new edition, but my article is not published. Is it legal or ethical to do this?
If they've accepted it, they will publish it (eventually). They have nothing to gain otherwise by holding your paper. That it's not been published in the latest issue isn't a sign that they're not going to publish your paper at all - they could for example have a lot of papers that are online ready waiting for an issue, and they've hit their page count limit for this issue.
Whether the journal has the authority to reject your paper after accepting it is a separate question. In principle, they can: nothing gets published without the editor-in-chief's approval after all, and he can change his mind. In practice, this happens extremely rarely. If they find out for example that the paper is plagiarized, then it can be rejected. But to reject it because they changed their mind about whether it's publishable - that's almost never going to happen.
I would check the journal on line. The Journal of Alloys and Compounds us a good example of several things that could be going on.
First, the front page is mainly about the available articles (this is a small portion of the section):
The first article shown is a "In Press, Journal Pre-proof, Available online" - it is accepted, considered in press, and the proofs have not come back from the authors. But, it is available to be read by anyone and the pdf tells you how to cite it since it has a doi already.
Now, go to the issue listing near the top of the page:
Notice that the 30 September issue is done and considered fully published. There are then three more issues listed as "In progress", being filled out with articles from the queue of available accepted papers. (Many/most journals prefer to try and balance the variety of topics covered in an issue, although some prefer to have focused issues. This impacts how long a newly accepted article might take to surface). Again, any articles listed in the "In progress" issues are fully ready to be downloaded, read, and cited.
So, go online and see what is available - your article may be there.
Yes, it is both legal and ethical. I don't know why you would ask about legality, unless you have paid for publication.
But there are two things here. It may just be a matter of timing and available space. Your article may be in the pipeline for a future edition, but didn't make it into the most recent. Except for a special issue, I think that is the most likely explanation.
You have a letter of acceptance from the editor, so I think that your article will appear and don't suppose an editor would pull your article after sending such a letter unless they learned late of some serious issue - say scientific misconduct.
But prior to a letter of acceptance, the editor is free to act and include or not include any article. The reviewers work for the editor, not the other way round.
You are free to ask, of course. You can send a message that you thought your article was going to be in the recent issue and would like a publication update.