Technically they should have gotten your permission, you are right. However, two factors come to mind, the adjuster may have been trying to expedite things at your convenience, and you do have a duty with any insurance company to cooperate and so the adjuster helped himslf to the liberty of going onto the property without your permission. Call the insurance company adjuster. The real issues here are the wrong VIN # and the dispute over the salvage of the car. See if you can reach an agreement, You're not going to score any points arguing over permission to go onto the property, unless there was actual damage done to the property.
This answer is provided for informational purposes only. Legal advice can only be given in an office appointment by an attorney licensed in your jurisdiction with experience in the area in which your concern lies.
Your issue is with the wrong vin number. You may want to let the insurance company know that it picked up the wrong vin number. If you notify the insurance company that it misidentified your vin number, and it still calls your car a salvage car, you should contact a lawyer.
Regarding the insurance company going on to your property without your permission, you could file a police report for trespassing. However, you may want to check the language of your insurance policy to detemine whether it allows the insurance company to access your property for such inspections.
In any event, you should talk to an attorney in regard to your car wreck before you accept any settlement from your wreck.
And, remember, in Louisiana, you have one year from the date of the accident within which to file suit.
Good luck and best regards,
Michael L. Barras