Steve is right that you need to talk to your insurance company, but there are some more things going on here.
First of all, when you sign a power of attorney (POA), that gives the insurance company the right, but not the obligation, to act on your behalf to transfer the title of the car. Have they already told you that they are going to total the car? If not, then they asked you to sign the POA in case they did, but they could still be evaluating the case. In that scenario, you still own the car, and you should find out what is happening to it.
If they have told you that they are going to total the car, then you need to find out what they are allowing as a value for your car, and you do have the right to discuss that value. The issue is how much you owe on the car vs what they give you for it. If they are allowing less than the payoff on the loan, you are going to be obligated to make up the difference. (By the way, if you have GAP insurance, this is what it's for -- making up any difference.) The fact that the car is totaled (and the insurance company has taken ownership?) does NOT relieve you of the debt obligation.
You should be aware that, technically speaking, the insurance company should not be able to pay off your loan without your written approval. That POA you signed probably does not extend to the loan on the car, just to transferring the title. There is a form you should be signing that says that you authorize them to pay off your loan. You should ask about that form, because the answer will tell you whether they are actually intending to pay off the loan.
If the insurance company has totaled the car and is taking possession, you need to get a written statement to that effect from them to prove that you are no longer the owner. Do not just assume they have taken ownership.
Also, if they are taking ownership, you should not cancel the insurance policy until you have it all in writing and get another car. It will probably be easier to get insurance for your next car if you already have a policy in place, especially since you just had an accident.