Vinted complaint: Won’t pay compensation

On 12 June I sold a skirt on Vinted. Buyer had chosen InPost so I dropped the parcel off at locker at Tesco Greenock. The parcel never arrived and InPost said this had to be dealt with through Vinted. This I did providing tracking number, copy of label used to send, description of how parcel was wrapped – a month later I was even asked what I was wearing that day. It is now over 10 weeks since parcel was sent and all I get from Vinted customer services is that they have to wait for the conclusion of investigation by carrier. Four weeks ago InPost sent me an email stating that they deemed the parcel as lost. I sent a copy of that email to Vinted and still get the same old excuse of waiting for outcome of investigation. I even wrote to the Head Office in London – needless to say no reply to that.
Sick of this nonsense- no skirt, no money. I am due compensation; their terms state this.