By default setting of your survey, the respondent can submit the survey more than once.
If you want only once response per responder, you can set this in your Survey settings. Simply by disabling multiple submissions.
How to disable multiple submissions:
Open you survey
Go to Get Responses and select Share settings
3. Go to Duplicate prevention and enable the prevention
4. Click on Save changes
Now, your survey can be responded just once by same person.
You can disable the prevention at any time, allowing multiple submissions per same person again.