So I found out that one of my old professors has published a complete rip off of a paper I did during my masters.
No citation or attribution to me, even though my work was published over a year ago. I published as a solo author.

He was not involved in the work, be we did have discussions and I did show him a preprint before I published. But he was never involved to a degree where including him as an author was even a question.

He has submitted it to a low tier conference where is a member of the organizing committee.

This is less than a year after I graduated.

What the fuck do I do?