Pro-seller timed me out on a damaged item

I bought a radiator valve a couple of weeks ago and it arrived as described. As soon as I put it on the rad and tested it, it threw an error and was clearly faulty so I reported it as damaged and it came back at me saying I needed to return it (at my cost) and wait for the seller to accept the return.

I immediately messaged Support as I didn't want to pay for postage. In the meantime the seller did nothing so I was unable to return it even if I wanted to. Vinted support sent me a 'taking longer to reply than normal' follow up but never got back to me.

Today we hit the 2 week limit and the item completed despite the open case. The issue has vanished from the item chat and I've now basically been scammed by this seller just because they're a 'pro'. What's the best course of action here? A charge back?

EDIT: If its not clear, the standard blurb told me I would have to return it at my cost, but in order to do that the seller would have to accept a return, they didn't they just ignored the case. There was no option to actually return the item.