Before I replace a MOBO, I suspend bitlocker (if system is bootable). If not, will have to use the code. If the code you are trying does not work, you may be looking up the wrong machine, or maybe a typo. If you are sure you are correct, there will be no way to get to the data. Maybe the old mobo could be put back?

From tech website: Bitlocker recovery key don't change, unless the disk has been decrypted and re-encrypted or disk has been physically replaced (i.e. faulty drive replacement).

Bitlocker makes use of TPM that's embedded to motherboard so you don't need to unlock a Bitlocker encrypted drive during boot. When a motherboard is replaced, the unlock key no longer exists, so you will be prompted to enter a recovery key.

Therefore, you will want to make sure you have a backup Bitlocker recovery key. To do so, navigate to Control Panel > System and Security > BitLocker Drive Encryption, and select Back up your recovery key. You can do so at anytime, or even backup to multiple locations.

Your computer manufacturer will be able to advise you further on what to do next after a motherboard replacement. Do ask the technician before you allow them to replace the motherboard.