Amazon's contracted logistics company refuses to pick up my return package

In late December I ordered an APC UPS via Amazon (Spain). It was an official order from the brand, however what I was delivered in early January was an old box. The UPS inside was dirty and not wrapped in plastic, had the stickers in the wrong places and both of the battery's poles had been plugged in during transportation (illegal). When I tried turning on the UPS it started making a loud metallic racket, so I turned it back off, unplugged a battery pole, put the thing somewhere non-flammable and requested a replacement from Amazon.

Amazon's replacement procedure seemed to work nicely as usual. They sent me a new unit via a good courier, which arrived a few days later. This one was definitely new and functioning properly. They also scheduled the pickup of my broken unit to a maximum of 3 business days later (time couldn't be scheduled, I just had to be available the whole three days, I guess), and claimed that if the broken unit wasn't returned within a month I'd be charged for the replacement.

Nobody showed up to pick up the replacement unit within 3 workdays. On the fourth day, in the morning, I received an e-mail from the logistics company in charge of the pickup saying they couldn't pick it up because: (blank). I called the logistics company, and the person I talked to located the pickup from the tracking number I gave them, said it was strange the reason was blank and also strange that I'd received the e-mail on that day, because apparently the issue was logged at a different time on their side. I clarified my details with them and they said the pickup would definitely happen on that day, the fourth day.

It didn't. It didn't happen on the fifth workday either. I called them again, and once again they located the pickup, confirmed my data and said they'd add a note saying the pickup had to be made.

Guess what? It wasn't. It has been two weeks now, and the pickup hasn't happened. The logistics company isn't contacting me, or visiting me, or notifying me, or scheduling anything. I tried sending a complaint through the local regulator of the transportation industry, but this is a slow process that can take up to three weeks to make progress. Meanwhile, I'm sure Amazon will happily double charge my credit card even though I only have one working UPS. I can't afford to pay for an extra, non functioning UPS.

There isn't much more I can do here since I'm not really the customer of the logistics company, Amazon is. But there is no way to actually contact Amazon and no process in their website to handle something like this. For some reason they have decided to contract with this company, even though they are - in my experience - pretty much always unreliable. Is there anything I can do? How can I get Amazon to collect my return package through other means, or at least not charge me again for the same UPS?