Insurance company sent me a letter saying I owe $6,000 to this accident I was in 3 years ago, I was at fault. whats gonna happen to me if I can't pay

The insurance company thatpaid out the plaintiff is now seeking damages from you to reimburse what they had to pay out likely becasue you did not have insurance or sufficieint coverage.  tis is commonly known as subrogation litigation.  you are liable to the insurance company if you were properly notified of the lawsuit and failed to have insurance, which triggered the plaintiff's uninsured/underinsurance policy.  te insurance company is going to continue to prosecute this matter and will likely file a lawsuit against you to collect the 6K.  i suggest that if you cannot afford to pay the $50/month, then you should call the company and provide it with a figure that you can afford to pay and simply stretch the payments out over time.  if you rather make ths debt go away by declaring bankruptcy, then you can do that.  however, i would first try to resolve this with monthly payments. if the nsurance company sues and get s a judgment it will be able to garnish your wages to collect the money owed.