I sent my paper to a math journal last August and I'm still waiting for any kind of feedback. I tried reaching out but got no reply. What should I do?

I think this is really two problems that can be separated. Each of them by itself is fairly routine to deal with.

1. A paper has been with a journal for an unreasonable amount of time, with no contact.

   This is pretty well addressed by Unexpected long delay with paper review and no answer from editors. You contact the editor (you have already done this), then the publisher (is that what you mean by "several people there"?). I would add the note that you should carefully investigate whether your spam filters might be blocking responses from them.

   If that does not yield a satisfactory response, your only remaining option is to withdraw the paper and submit elsewhere. I know you don't want those outcomes, but there isn't really anything else to do.

   Contact the editor and publisher only by their publicly available contact info, which in addition to email could include phone, postal mail, etc. There isn't any way beyond this to "force" an answer. Visiting the journal headquarters would be borderline "stalker" behavior, and in any case won't be helpful; the people responsible almost certainly don't work there in person.

2. You want to publish a Paper #2 that relies upon an earlier Paper #1, which has not yet been published (for whatever reason).

   This happens constantly in mathematics for much more mundane reasons (long review times with response from editors, multiple rejections, etc).

   There's a simple and well-established solution: you post a preprint of Paper #1 (which it seems you have already done), and you submit Paper #2 citing that preprint. If Paper #1 ends up being published before #2, you simply update the citation in #2; if not, you leave it as citing the preprint. That's very common and will not raise any eyebrows.

   I'm frankly surprised that your advisor seems baffled by this. I'd think any professional mathematician in this day and age should be quite familiar with this situation and how to address it.

If you do end up deciding to withdraw Paper #1, you can consider merging it with Paper #2, but only if you genuinely think they are better as a single paper. If not, it's fine to just continue submitting both papers separately.

• If you haven't already posted an arXiv preprint of #2 at that point, then don't withdraw #1; rather, replace it with a updated version that includes the material from #2.

• If you have already posted #2, then see Standard practice when merging papers on arXiv you should withdraw one of the papers (with a comment that it is being merged), and update the other with the merged version.