PhD Admission Mistake, got unconditional offer but got rejected simultaneously

I applied for a PhD studentship at a Russell Group university for 2026, the same year I would graduate. After consulting with the PI, I was encouraged to proceed with my application. Here’s the timeline:
- Submitted my application, indicating the PI's name, studentship name, and student title.
- Day 7: All referees submitted their letters of recommendation.
- Day 13: I received an email titled "Information about your offer." In this email, I got a student ID and was informed that I needed to upload an official interim transcript to receive the conditional offer on the site. I also needed to provide the final transcript for the unconditional offer, and once I uploaded my graduation transcript, I would receive the unconditional offer. Additionally, they advised me to provide the graduation transcript as soon as i obtain it to proceed with visa preparation.
- Day 17: I submitted the interim transcript. The grad admissions office was supposed to review it and then send it to the PI.
- However, on the same day, the admissions office mistakenly thought I applied for 2025, even though I clearly stated I was applying for 2026 and had confirmed this with an admissions officer.
- Day 18: I received a rejection email stating that I wouldn't be graduating in 2025.
- Day 19: I reached out to the department and the PI, who said the offer wasn't made by him and suspected it might have come from another academic.
- Day 20: I feel completely lost and unsure of the next steps. I applied within the deadline, fit the criteria, and the grad admissions office didn’t even forward my application to the PI because they thought it was “too early.”
What should I do next?