Check first that you have received several different alerts as opposed to a repeated alert. Additionally, check if another app on the device is notifying you of a single alert.
If you are receiving repeated alerts of the same message, your device may be set with a REMINDER feature, this may cause the alert to repeat until you acknowledge it. This feature can be turned off following directions in your device’s User Guide. Your wireless service provider will also be able to provide assistance.
You may also be receiving the alert through an app such as The Weather Network or MétéoMédia, which both distribute alerts.