I really don't know what to...

For context:
I sold a set of automotive wheels for around €600 to a guy in the USA and decided to ship it with Hermes BorderGuru (what a mistake). I ended up paying almost €200 for shipping with them and after paying the label online, they provided me with a "retoure" label. When I went to a Hermes PacketStation (gas station close to my house) and dropped the package, I asked the lady "why the hell is this a retoure label? I just want to ship this to the receiver in the USA". She replied with something like "that's fine, doesn't matter", so I believed her and dropped the package. This was on the 21st of February 2023.

After a tracking it for a couple of weeks on Hermes' website and not getting any new updates, I decided using another website (like parcelsapp.com) where it showed me more detailed information. But still, since the 27th of February the package hasn't moved and ever since I've been trying to call and email them, with no success.

Around the beginning of March, someone picked up my phone call and basically said "oh we had a problem at the sorting center, you will receive your package back in 5 working days and a Gutschein as an apology from us", which was obviously a lie.

After a few days, somehow Hermes' tracking page started showing that my package was delivered (Zurück beim Absender: Zugestellt) while showing the last update as "Die Retoure wurde von Hermes übernommen" on the 22nd of February, which is totally not true. ParcelsApp is still showing the package as in transit since the 27th of February.

Then after weeks of being on the dark, someone answered one of my emails a couple of times on the 27th of March stating that the description of goods I provided was not enough and that they needed a HS-Code (Zolltarifnummer), which I researched and provided them. I was asked to confirm this number, but that was the last time I heard from them.

Now recently, the buyer opened a case on PayPal (rightfully, since he didn't get what he bought), which forced me to refund him of €600. Now I'm left with no package, no money for them and no money for the shipping.

To me this is absolutely unacceptable, but I'm not sure what to do since contacting Hermes always results in "you should contact Hermes BorderGuru, not us", which results in nothing...

Does anyone have a suggestion on what can be done from my side?

PS: I have sent other packages containing the EXACT same wheels with UPS after this issue and did not have a problem.

TLDR: Hermes BorderGuru scammed me of almost €800 and they completely ignore me. What to do?