Bump to add solution:

I had the same problem after changing telco by MNP from digi to xox. Cannot receive TAC from bank after that.

After googling, I found this suggestion from this website:
www.facebook.com/Maybank/posts/saya-dah-tukar-telco-dari-maxis-ke-tune-talk-nombor-saya-masih-kekalkan-no-lama-/758875677478597/

Cara Update TAC selepas MNP ke TUNETALK HT
RHB Bank
Taip UPDATE hantar ke 66300
Bank Islam 66399
Taip UPDATE hantar ke 66399
Maybank 66628
Taip UPDATE hantar ke 66628
Bank Rakyat 66300
Taip UPDATE hantar ke 66300
Bank BSN 68886
Taip UPDATE hantar ke 68886
Dalam 24 jam sudah boleh request semula TAC


I tried it and it works and can receive TAC after less than 1 hour