Why do renewing customers have to re-enter detail

WHY DO I HAVE TO RE-ENTER ALL MY PERSONAL DETAILS WHEN I WANT TO RENEW A MEMBERSHIP ONLINE ON YOUR WEBSITE. ??? You already have all of this info but you ask for my membership number and then I have to from scratchre- enter all my details again e.g. age, date of birth and,and,and... This is the shoddiest, worst system I have ever come across. I complained about the same thing a year ago but it falls on deaf ears.