I edited the copy for the email the respondent gets once completing the survey. I did this a few months ago. I just tested it and see that respondents are still getting the original email.
How would I fix this?
It sounds like when you edited the email, you updated the Plain Text Version of the email body. You will also need to edit the HTML version of the email body as that is what the majority of recipients are receiving.
Here is more info to help: