Describe the change, without forcing it.
Mention when the problem began, whether it affects one door and whether the door sits normally in its frame. There is no need to force a key or repeatedly work a damaged lock to gather more details.
If you mainly want old keys to stop working, rekeying may be the more relevant conversation. For an entrance used by staff or customers, see commercial locksmith help.
Think about when it happens.
Does the key turn while the door is open but catch when the door is closed? Does the handle feel loose, or does the latch miss its opening? Share an observation you already have; you do not need to keep testing a damaged lock.
Tell us about recent changes such as a new handle, a door that has started rubbing or a key that looks bent. The recommendation may involve the lock, its fit or another part of the door. Discuss the scope through our estimate questions before authorizing work.