What steps can be taken against a rehab facility that was abusive by neglecting a patient?

My husband had knee surgery over two months ago. He was unable to stand or walk so he was sent to a rehab. We thought it would be a week or two for him to recover his strength and return home. He was there for over 2 months and never recovered the ability to walk. With Covid-19 we could only visit standing outside and talking thru the window with cell phones or writing notes. Saturday I visited and discovered him in pain, and crying out for help. I went to the office, had him removed, and took him home. That afternoon I had to call 911 for him to be taken to ER. He had lost over 30 pounds, had infection on his head(a cancer removed), a urinary infection, advanced dementia, and a bleeding mouth caused by lack of fluids. My family and I were lied to about his progress and care at the rehab. We were told several times about the great care they were giving him. Others died at rehab and they were probably left to die alone just like my husband was. We hope he can recover from rehab.