You receive two sets of keys of which one serves as a reserve. Keep this set with someone who you trust. Have you locked yourself out or have you lost your keys? This is what you need to do:
Spare keys
Pick up your set of spare keys at the person who keeps them for you.
Key service
If you are unable to pick up your spare keys then you can contact a private key service. They can remove the old lock and put a new lock in your door. You must pay these costs yourself and not De Key. Make sure you also get a new spare set of keys, so you can hand in two sets of keys to De Key once you move out.