Vinted review: Vinted 'sold' an item twice, made it v difficult to contact them, closed my query without resolving

I am furious with vinted as they did not deal with the issue I raised, said it was closed when I told them this, and have generated auto negative feedback when it is a problem CAUSED BY VINTED. They had clearly not read my complaint as their response said they'd send me a label to post the item! It was not a solution to my issue which is that they ' Sold' my item (jaeger trousers) to a member (and I sent it off to her) then moments later also 'Sold' it again to another member. I wrote to this 2nd 'buyer' explaining Vinted's error. Since then I have been plagued with messages from Vinted about sending the item to this person culminating in one saying I had failed to send it and Vinted would be refunding the buyer. It is impossible to contact Vinted directly and they closed down my query without resolving it. How can anyone get Vinted to deal with an issue which suggests they need to correct their systems and has caused me a lot of hassle all for £3! Thank you for reading this.