Lost package due to Colissimo but problem resolved according to Vinted what to do?

A month ago, I shipped a package via Colissimo to Belgium. This package got lost. When I called Colissimo, they told me that upon arrival at the Belgian border, they handed the package over to DPD. And that I only had to call DPD in Belgium. My response was that on my end, I didn’t know about the agreements they had with DPD and that I only knew Colissimo. That I shouldn’t have to call anyone other than Colissimo. Because it is not noted anywhere that when shipping items abroad, upon arrival at the border, another organization takes over the package. In any case, this package has still not been found and Vinted just replied to me that the problem has been resolved… I don’t know what they call resolved because the buyer received nothing and I haven’t been paid. Has anyone ever had this kind of problem? And if so, how did you resolve it? Thank you.