Amputation of the toes

I had to have my toes amputated after the unsuccessful treatment. The accident occured at work but there was also the doctor's mistake. The employer's insurer sent me the letter tht i should claim from the hospital from now on and they will not compensate anything. This is stupid as I would have never went to the hospital if the accident hadn't occured. In fact my injury was caused by the employer's negligance and asking me to work on the broken machine, which has been already prooved! Should I have the lawyer to appeal or it is enaugh to send the officiale letter to the insurer in which I give my arguments?