Vinted complaint: Item damaged in transit

When I collected an item i bought on Vinted, the parcel was covered in petrol or diesel, it had a strong smell. The assistant advised me open it with care. I took it home hoping the packaging had protected the coat inside, but despite having 2 layers of bubble wrap the fuel had seeped through and damaged the coat. I immediately informed Vinted and also the seller, attaching photos as proof. Vinted initially sent an automated message, followed by another message with instructions to send photos and a description, assuring me that it would be dealt with. The transaction was not cancelled and after a few days I noticed that the seller had left me feedback which had ended the conversation with Vinted. They will not accept any further enquiries stating that I had completed the transaction, which I did not. Now I am left with a coat that I cannot wear.
I have successfully bought and sold many items on Vinted, but am very unhappy with the lack of communication from the support team.