Hopefully you got the vehicle plate number and a name and call the police and report the accident as soon as possible and give them all them information you have. I would treat it as a hit and run if I was you.
You need to call a Texas attorney ASAP who can look at other possible areas where recovery might be made. For example a product defect case against the vehicle manufacturer. But these type cases need to be worked up quickly as evidence can disappear or be destroyed and reduce your chances of recovering. I would be happy to take a look at it.
Unfortunately, your medical doctors may correct. I would contact an attorney who specializes in personal injury litigation. They may be able to best assist with you regarding any communication with your doctors. Further you should discontinue any communication with the insurance adjuster until you had your consultation with that attorney.
Your best bet is to contact a personal injury attorney. There are a lot of moving parts here. Venue should be explored on the driver and the companies contacts in the United States. Worst case scenario you have to go to Canada. Either way these cases are heavily defended, you are way behind already.
Typically, auto insurance should cover this type of damage. Whether its the car owner that caused the damage or the auto insurance of the owner of the car that was damaged. As a practical matter you should contact your insurance carrier and make them aware of the situation and get their advice.
You can hire an attorney and file suit against them immediately or let you auto insurance take care of the claim thru your collision or Uninsured Motorist coverage. The insurance company for the guy who hit you might be looking for way to not allow coverage because they are not cooperating.
Your carrier can pay your claim then they can decide to go after his insurance for reimbursement, but at that point you will be out of the process other than to cooperate with your own insurance...