That bug is fixed. Now it's not possible to delete a survey that has been answered.
However, you need to add a couple of surveys (they can just have some filler text for the questions and answers and should indicate in the survey header that it's a defunct survey) so that the next *real* survey you make doesn't re-use an old number.
Register for free to join our community of investors and share your ideas. You will also get access to streaming quotes, interactive charts, trades, portfolio, live options flow and more tools.