To no longer receive engagements on a contact channel, you can delete the channel from a contact. Deleting the contact channel removes it from the contact's engagement plan. If you delete the only contact channel for a contact, you won't be able to engage that contact during an incident.
See https://paws-r.github.io/docs/ssmcontacts/delete_contact_channel.html for full documentation.
ssmcontacts_delete_contact_channel(ContactChannelId)[required] The Amazon Resource Name (ARN) of the contact channel.