car and the park unlock won't function with your foot on the brake, check your brake lights. This would normally require a second person behind the car looking at the lights. If your brake lights don't light up when you're experiencing the issue, then you can be fairly certain the brake light switch is the issue.

If the brake lights come on normally when you press the brake, but it won't come out of park, then it's a different issue (possibly a solenoid issue).