I had similar. My ex thought it was entirely my responsibility to send the dc to him with a suitable wardrobe for each visit, which he would then keep - just to piss me off, I think, I can’t see what else he got out of it…
When the kids were too young to sort out their own stuff, I made sure I packed clothes for them that I was happy to never see again - anything that was about to be outgrown, or was scruffy. I did a lot of charity shops, & also let friends know that I was very grateful for castoffs. (This annoyed ex as we had various mutual friends whom he didn’t like knowing he was a dick).
Once they were old enough to notice & started wanting to take their ‘good’ stuff, I just held the line that if they left anything at Dad’s, they’d have to go without it until their next visit - if that meant wearing their less favourite trainers or not having make up for a party, oh dear.
They very quickly got very good at organised packing, which is now standing them in excellent stead as young adults.
Meanwhile, I assume xh’s house is now bursting at the seams with long forgotten second hand Asda tshirts from when they were 8 🤷🏻♀️.
I think it’s all you can do - they’re teens, they’re old enough to understand that Dad won’t buy them stuff, & you will, but you won’t buy it twice, so they need to pack a bag when they visit their father.
Mine have a fairly low opinion of their DF as adults, & bluntly, a good chunk of that is because from an early age they had his measure as a selfish arse who resented providing for them.