What did you tie them to?
I have two small screws on the side of our posts where the actual lamp attaches. So I use two twisties that I bring around the post and then tie to the screws on either side. It gets very windy here too but that's always held them in place.

Each bow comes with a twisty tie so I just wrap it around that little ball at the very bottom as tight as I can but again, when it gets windy it doesn't stay put and I end up chasing them down the block. LOL

Yeah, that's not gonna work.

You need to attach the bows to the rod? (don't know what it's called) that's attached to the back plate.

I use string to tie my outdoor bows . One year I used wire and the wind bending the wire on the bows back and forth broke the wire.