Nursemaids arm at daycare

I am so distraught. My son is 2.5. He was completely fine yesterday morning. I got him out of the car and walked him in to daycare and he was fine. He did his normal cry and tantrum because he didn’t want to leave mom at drop off but this has been normal recently. I thought everything was fine. I did not receive any calls from daycare all day. When I picked up my son he was just sitting on the floor crying. They told me that he wasn’t himself all day. He didn’t want to eat, didn’t nap, didn’t want to go out side (he loves outside!) and whined all day. They said they thought maybe he had a stomachache ache and wasn’t feeling well. He screamed to leave (now realizing it was because I was trying to hold his had to leave). By the time we got to the car to leave I realized his arm was completely limp. He wouldn’t move it and he screamed when I moved his arm to buckle him in his seat. I took him straight to urgent care and he had nursemaids arm and they had to pop it back into place. How this happened isn’t even a issue anymore. The issue is they left him in pain all day and didn’t call me! They said he had been screaming since I dropped him off! 9 hours and you didn’t realize his arm was limp and he was in pain! My heart hurts and we are home today. I couldn’t send him back. We called daycare right after leaving urgent care and they didn’t even know what nursemaids arm is. How! I’m thinking they pulled his arm at drop off when he was crying for mom when I was leaving. I’ve seen this girl pick kids up by the arms before!