Injured by the worker from other company

The workers of some company where unloading the boarding on the hight of 5-6 m. They were in rush, very careless, without paying the atention to wthe fact that workers from mycompany (among them I) were on the lower positions. They threw on element of the metal boarding. I was hit on my head and neck. The weight of this element is about 30 kg (considerating the hight I recieved the 100 kg on my head). It hurt my head and forearm. I had breakage of the forearm including squeezing of the tendons. They put the plaster splint on it but onlywhen i visited my first contact doctor!!. They only cleaned the bleeding head and put the elasic dressing on it at the hospital.

To the hospital I was driven by the manager of the other company. After the accident it took me about 30 minutes to be able to walk to his private car. Nobody called the ambulance even though I insisted on it. My manager sent me back home saying that I will be ok within few days.

How to claim n my case?