If you have sent the questionnaire via the internet, you will immediately receive a acknowledgment of receipt in your browser. Did you not receive an acknowledgment of receipt? Then please check whether you did not accidentally use the 'Save' button instead of the 'Send' button. Log-in (if necessary), go to the last screen, and press the 'Send' button. Did you recently completed and submitted the survey on paper, then it could be that your submission and the reminder letter have crossed eachother.