Dell has had such issue with this tablet's charging/data port, I imagine that the warranty support staff is trying to do whatever it can to avoid claims. Yes, it's a user issue if the port's pins have been jammed down by someone trying to push in a plug the wrong way; but no, if this otherwise is a parts issue. And how could the warranty people even know without looking at the device?
As noted above, unless this was a user-error issue, you're covered by warranty and should pursue, forcibly. The next call, ask nicely, and forcibly, to have the issue escalated to the supervisor. That typically fixes these front-line-person issues for me.
And no, a charging port breaking down of its own accord in under 6 months is not "normal wear-and-tear." So Dell is making tablets, now, that need to be replaced in 6 months? Right.