Rearended by a second car that was hit by a third car.How to han

HI, I was rearended by another car on a busy freeway on Friday.  It was rush hour and There was traffic jam so all the traffic stopped.  I stopped too. But the third car didn't(the driver said there was something wrong with his clutch).  So it hit the car behind me and the second car hit my rear bumper.  I was driving a two month old Toyota Corolla that was just bought for my son!  I didn't call police because the second driver was a young man who begged me not to call since his driver license was suspended and he would be sent to jail if the police came.  The third driver is a Mexican with his wife. She was crying. Their car was undriveable and had to be tolled. They might be illegal immigrants so I had pity on them. Also both cars have insurance. And a kind woman drove off the freeway and told us she was the witness seeing the third car hitting the second car and gave us her number and address as a witness.  I called Geico and they said it's not necessory to call police.  So anyway,my rear bump's paint got damaged. My lower back hurts. And my left leg and foot are numb and weak. My neck hurt and I have headache. The urgent care doctor said it was normal but no bone fracture. It's only muscles so he gave me some medication and said the symptoms will go away. But I am thinking it's scaitic. 17 yrs ago I was thrown off the bike because a motor cycle hit me. My tailbone was broken and my back was hurt too.  It took me two years'to recover.  This time it isn't as bad as last time at all but I think it may make my 腰椎間盤突出 a little more. The third car was said to be at fault by my insurance but their insurance is not a good company at all.  Geico(I just switched to them two months ago to save money on my new car and my old company is a lot better at handling claims) rep said I can use my own insurance and pay my $500 deducbile and they can ask the other insurance company for reimbursement but they may not get it because of time limit.  Or I can contact the third driver's insurance to ask them to fix my bumper.  I thought Geico should contact the third driver's insurance company for me. Anyone knows what the procesure is?  I've never had a freeway accident before so I'm shocked and my necked is stiff just using the computer. Please share your knowledge.  Thanks.