Vinted complaint: Vinted didn’t resolve my issue but keep closing the chat

I purchased an item from one seller and it didn’t work. Told the seller about the problem and she asked to have it returned rather than reported as SNAD (not as described). Agreed to return the item when seller pay the postage but after the return initiate, the seller ignored my message and didn’t pay for the return postage either. Contacted Vinted customer support for help but they didn’t do anything but told me just to download the label and drop it off (???) then just close the chat so I can’t send my reply (???). I don’t ask about how to return an item, but ask for your help!!!! At least try to contact the seller and ask why she keeps ignoring my message and doesn’t pay for return postage while she promised to. If she doesn’t pay, I’ll have to pay for it while the item is completely broken (doesn’t work at all). How can it be fair to buyer on Vinted?