Paper Withdrawal before Publication - Can I send the paper elsewhere
As long as you can prove that you withdrew your paper, you can submit to another journal. The possibly delicate point is with the proof.

I would think that in case the first submission comes up, any sensible editor would take a copy (with all headings) of the emails you sent to withdraw as a decent enough proof. Moreover, what you describe points to the first journal being predatory, which might be easy to decide for the second journal editor depending on how obviously predatory it looks. Then the first journal would not have much credit, even if they would go as far as forge emails.

If you want to be completely safe, you can mention in the cover letter that you submitted your paper to another journal quite some time ago, and then decided to withdraw it (precise that you mentions this because the first journal never answered you emails). It would make your case bullet-proof in case the first submission ever comes out. This might not reflect too well on your submission however (it might prompt the reason why you withdrew, or it might make the editor fear you could withdraw again while he or she bothered to get a report), but I would not think it would have a significant impact.

Last, it seems you might have submitted to a predatory journal, and that would mean you should have been more cautious. If you don't know a journal, don't publish there without getting an opinion by someone well established knowing the journal.