Your survey is activated from the moment it’s created. You can manually disable answer collection ifyou no longer want to collect answers, or you can set an automatic deadline after which the answer collection will be disabled.  

Navigate to the main screen with all your projects (My surveys). Find the survey you want to deactivate, click the three dots “...”, and then click Unpublish survey

Deactivated surveys are not deleted, and can be reactivated when necessary. They will remain visible on your dashboard but cannot be answered by respondents.

You can also disable answer collection from the survey’s settings, which you can find by clicking on Settings in the top menu after opening your survey from the dashboard. 

Tip: If you didn't manually suspend the survey, but it has stopped collecting answers, make sure that you didn't activate Automatic response collection deactivation.