Rear Seat Belt problems of the 2003 Infiniti FX35

My daughter six years old was in the passenger seat in our family car. There was no car accident , but when we arrived home we were unable to release the seat belt . In fact the more we tried to release the seat belt , the tighter it got. My daughter was trapped very hard in the seat belt. We been trying to release her in many deferent ways, it doesn't work. She start to cry and scream very loud and her stomach tight up more and more with the belt. There was no other choice, I took knife and cut out the belt. After she vomited and complained of abdominal pain.