@RaeParks18 It's okay, I don't mind the rant...
I agree with your father, to an extent. Personally, if you have a manuscript or any other body of work you would like to get published the traditional way [through a publisher], I wouldn't recommend sharing it online either unless it was already for sale. (None of the books I share on here are ones I don't think would ever get stolen, even though I fully believe it is Wattpad's responsibility to protect them.) Because there's always that risk. Yeah, it's easy to gain attention on writing apps now, but it's also easy to get plagiarized or stolen from. And it's harder to protect them when you don't have a huge agency or a licensed copyright.
BUT none of this is your fault. Someone in your audience betrayed your trust and that's on them. Screw that.
Please keep each and every proof you have that YOU are the one who posted your work FIRST (which is imperative that you only unpublish and not delete your work), and don't feel disheartened by this incident. You'll get past this.
Stay strong!