this happened to me a few months ago, i got in contact with the seller and the person who'd received my item (and i hers) and we asked the seller to reimburse us for the shipping costs. it required a lot of trust between us but i eventually got my item, she hers and the seller reimbursed us for the cost.
when you file the complaint/report with vinted there's an option which says something like: came to an agreement and there i wrote that the seller had agreed to pay for shipping costs.