UPS not paying me back.

Hi, I bought a bike through the German eBay Kleinanzeigen and because the seller didn't want to deal with the sending of the bike, I had to order UPS to pick it up for me. I filled the online form and I got an estimate of 160€ for order of the service. After everything was alright, the bike came but after a couple of weeks the seller contacted me that he received a bill for almost 1200€ from UPS. Looking at my bank statement I notice that the 160€ were never booked and I guess UPS assumed that was the seller who order the service. I transferred the 1200€ to the seller after this he transferred them to UPS and did a reclamation. I did a reclamation from my side too and explained the whole story. We didn't get any positive answer until I called them one day and then I was finally confirmed that this must be a mistake and they will re-check the bill. Because of no answer I called them after two weeks again and I was told I should get almost 1000€ back. After which I asked if I can get a confirmation per email.

Now it has been since the end of August I got the confirmation. I've been calling them 3 or 4 times since then and it's always the excuse that they need to follow up in their system and they will contact me.

Has anyone an idea what I can do more? I'm living in Germany.