I'm so sad that I now have faced this problem, too. (Headphones not charging, the red light switching on for a couple of seconds and then nothing happening.) I can now only use my all time favourite headphones connected to my laptop with the USB cable. And it looks like there is nothing you can do.
Hi Emilia,
There's nothing you can do. It was a defective product. Unfortunately, there was no warranty, and now there is no available authorised service for the product. If you're brave enough, you can dismantle it, and maybe you can find the component that requires replacement. I tried, but I couldn't fix it.
It was an auspicious product. I could say one of the best headphones I've ever had.
Kind regards,