Sometimes, a door or other station will place a call, but continue to ring after the call has been answered. Here are some common reasons this might happen.

1. The call might not have actually been answered. When an IX-MV7 or other answering station receives a call, there will be a touch screen or physical button to dismiss the call. This does not end the call on the calling station, it simply opts the answering station out of the call. The system operates like this to support systems with multiple answering stations. This is almost always the reason, even if the end user says that they are answering the call.
   This can even be done on some models (IXG-2C7, IX-MV) after unlocking the door. Hitting the door release key, then hitting the dismiss button, will unlock the door, but it will not end the call. 
   The solution is to make sure that the call is always fully answered before unlocking the door and dismissing the call, either by hitting the appropriate button on the station, or picking up the handset. This may require some minor training for the end users.
2. If you observe calls being fully answered and the door continues to chime after the answering station hangs up, there is a chance that the call acknowledgement from the answering station is not getting back to the calling station. Isolate the two stations on a PoE switch off the network and see if the same behavior persists. To see which ports and protocols the system utilizes, the network administrator can consult the Network Security Summary. https://know.aiphone.com/ixg-support-tool-application-notes/ix-%7C-ixg-series-network-security-summary