How to I dispute a denied claim by my employers insurance company ?

I believe I was injured on two separate occasions ,a week apart , on the job , while performing heavy lifting and pushing carts for long periods of time. Pain from injury did not manifest until middle of the night. I informed my employer after the 2nd incident that I wished to file a claim as I was injured twice after performing the same tasks while on the job. I received no training or guidance for performing these tasks. My claim was denied even though injury was verified by designated Doctor. I have been injured now with severe pain and inability to drive or work for over three weeks and have no access to medical care.