You’ll be surprised to learn that GoDaddy’s reps don’t always have accurate information, or sometimes don’t provide the information in the right way. I suspect what they have been attempting to say was that you can’t have a www if it conflicts with an existing record (for example, a CNAME or another A record). In other words, if the DNS is told to go to two different places for www, it won’t work. I’ll try to get a screenshot of my DNS and postb it for you