This is fixable. You can unbrick the device by flashing this binary at 0x08000000 (the flash base address):
https://files.zubax.com/products/com.zubax.telega/com.zubax.telega-1-0.3.68620b82.compound.bin
After the binary is flashed, the device may refuse to start with a missing signature error. To fix that, we will need you to tell us the unique-ID of the board which is stored as 12 bytes at 0x1FFF7A10. When we know the unique-ID, we will tell you the digital signature of the board that you will need to write at 0x800bf00.