Hi Martin,
I hope you are doing well!. I'm Jhun, an independent advisor. Sorry to hear that your having a problem with this. Please let me assist you.
You've mentioned that the company longer exists, the other way you can do is contact Microsoft Support for Surface Pro, they can reset the UEFI password, but if only you can provide a valid proof of ownership of the device.
As of now, there's no safe way to reset or bypass UEFI password, since the Surface Pro 5 don't have any CMOS battery that we can use to reset it.
Best Regards,
Jhun