What devices do you have listed when you go to Settings > [name on top], and scroll to the bottom? Those devices can change your contacts that are stored in iCloud. If you are sharing your Apple ID with anyone else, then remove them from your account and change your password.
Also review the Accounts you are syncing with your Calendar app by going to Settings > Apps > Calendar > Accounts. If you are syncing any Calendars from a Google account or Microsoft Account, then Siri will capture any information provided from those Accounts as a possible suggestion. Also note that those accounts can also sync Contacts and can be changed from that same Settings location.
This is also true for any Email you received where that email address appeared and your name was mentioned. They are just suggestions and does not mean that the person has access to your account.