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 spare set of keys at the person who saves them for you.
Key service
If you cannot 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 (and not De Key) must pay these costs yourself. You also need to arange a new set of spare keys and give these to De Key once you are moving out.