Should I contact the journal because I am not receiving a response after a year? I have submitted a paper to a Springer mathematical journal. The reviewers asked for a revision, and after revising the paper, the editor's decision, alongside with the reviewers' one (of course), was to accept the paper. In the email that I have received it was stated: "You will receive an e-mail in due course regarding the production process". But after that, a whole year has passed and nothing happened. No info after that email. After logging into my author's account, on the main menu in section Completed I can only see:
 - Submissions with a decision: 1
 - Submissions with a production completed: 1.


Generally, what does production completed means? I read about MyPublication service on the Springer website but I never had a chance to see the questionnaire. Just to mention, I did not get any info, nor doi number, nor anything similar. Only that the paper is accepted, a year ago.
Should I write to the journal? To the Editor, the Editor-in-Chief, or some service to inquire about my paper?


There is a similar question (Springer special issue status) but it regards the special issue status. In my case it is a regular one. Also, the comments and answers on that thread were not helpful in my case.
Yes, after a year you should definitely write to the editor and ask for an update. 

Production completed likely means that the paper is actually ready for immediate publication either in print or online. But check, nevertheless. Print, especially, takes a while to get out the door. But even online publication takes a while to move from staging to final servers. 

But, yes, ask.