Creditors are allowed to engage in self-help to repossess cars, but that freedom isn't without limits.
If a creditor risks "breaching the peace," it isn't allowed to repossess the vehicle. So, the repossession agent can't use, or threaten to use, force or violence. It can't break locks or destroy or damage property in attempting to reach the car.
If the repossession agent breaks into your garage to take the vehicle, that is breaching the peace. You can raise that as a defense if the creditor files a deficiency lawsuit against you.
You might also be able to file a counterclaim for any damages that the bank or repossession agent causes, including damage to your garage and locks.
To get past that locked garage legally, the bank will probably have to get a court order that requires you to turn the vehicle over. This is called "replevin."
Keep in mind that if the bank gets a court order and you don't turn the vehicle over to the bank, then the local Sheriff might be the person breaking into your garage to take the vehicle.
For more information about car repossession and replevin laws in your state, consult with a local attorney.