I'm sorry this happened to you. How long ago was your surgery and when was the hydronephrosis diagnosed? Are you under the care of a doctor other than your hysterectomy surgeon? I know this can be a very serious condition but don't know much about it. This article may be helpful - https://urology.wustl.edu/patient-care/reconstructivesurgery/urologic-complications-from-surgery/.
I had different complications (bowel problems) post-hysterectomy and had a hard time getting proper help. I hope your experience is better than mine.