I have been working in a company for 1.5 years and an employee took up a position in another department, which caused my department to be short staffed.

Meetings were held and I was told that I would not be affected by the change and that the replacement will fill the vacancy. The day that the new hire arrived, my supervisor sent me a message on Teams to tell me that I had to train the new hire, do the tasks of the vacant position in addition to my normal duties. I was upset and complained alot about the workload and not being told anything about this before. She laughed about it when I brought it up saying that "I'll learn to manage the work". Training was completed with the new hire and I heard a rumour that I will have to do the duties of the vacant position. My supervisor nor manager never communicated with me about the change. I only received an email with the new duties after a coworker told her that she was "unfair " for telling others about me getting the new duties and not telling me directly. The workload is unbearable and does not come with a pay increase. I have been so stressed and unhappy in this new role ever since. They never informed me and I was never asked nor publicly considered or told that I would have to do the duties of the vacant position, while the new hire does mine. How do I cope with this job until I find something better?