My Co-author made the mistake of sending a research article to a predatory publisher(OMICS), which got accepted after 2 months of review. On the same day of their acceptance email, we sent a withdrawal request mentioning that there were serious concerns with the results of the paper(We lied). No contracts were signed, no fee was paid and there was no transfer of rights etc. They requested a fee of 300 USD for the withdrawal process. I ignored their email thinking that they won't publish the paper as no contracts/money was involved. Fast forward, a few weeks ago they have published the paper on their website on our name with the complete DOI and all, whereas the paper is already in a review process for another journal. What should be my next step now?

Unlike the previous question cases, my paper has been published on their website without any fee