Every bank has their unique account numbering. So far in my past career working with banks, no banks in Malaysia have conflicting (or rather, similar/matching) account number setup.

RHB has 14, and that is set. They wouldn't have any extra or lesser (referring to CASA), and BSN has 16. Ultimately, you will receive your refund. IBG is sort of manually processed, that is why the transaction is accepted for processing in the beginning, only to be declined at a later time.