Welcome to copyright hell! Mua-ha-ha...
More seriously, though, do the following in parallel:
Copyright re-acquisition and free publication
I assume that just before signing the accursed "copyright form", you gave a copy to someone else, and agreed to grant him/her rights of copying, distribution, and subsequent granting of the same rights (e.g. you licensed your work to them under one of the free licenses, such as Creative Commons or GNU FDL etc.). If you think this did not happen, try jogging your memory a bit, I'm sure it will come back to you. And I'm sure that person will later be able to attest to this having happened. Now, have that person make you a copy with the same rights you gave him. You can now publish that copy wherever you like, and IEEE can't do anything about it. Also, in practice and from (limited) experience, IEEE doesn't try to harass authors who publish a copy of their work for free online. (They might come after you if you publish it commercially somehow.)
Interaction with IEEE
- IEEE Explore (I'm sure they have a contact form)
- The conference chair, or whoever is personally in charge of the conference proceedings (check on the conference website)
and ask them why the proceedings have not yet been published, and to try and make that happen ASAP.
I'll add that, personally, I don't consider a "publication" on IEEE Explore as a publication per se, because people who didn't pay the IEEE (a significant amount of) money can only get your paper via SciHub, which doesn't always have absolutely everything available, and some people are worried about the legality of getting papers through there. So it's important you also follow the parallel course of action and properly publish your paper online - make it accessible by the public.