It might appear strange to you, but this also happened to me when i ported to another telco.
When i contacted the bank, i was told I had to update them once I mnp-ed even though the hp number remained the same.
This happened a few years ago, not sure if things have changed.

Using TAC via SMS is the most convenient to majority of users as most of us carry our phone all the time. Some banks use hardware token and allow users to choose either sms or pin generated by this token for most banking transactions.

I know of at least one bank in Sg that requires a hardware token plus hp sms combo if you perform a more "risky" transaction like adding new favourite payee or sthg like that.

The issue with TAC usage in Msia is they are not very reliable when it comes to receiving the sms with tac. As with most things here, we've come to accept it as it is. I've personally lost the opportunity to purchase ASNB unit trusts online a few times because the TAC never came or arrived after time-outs.

I don't know whose fault it is. As for receiver location, we can only depend on the signal strength indicator of our phone. SMS has existed since the first time I got a mobile phone in the nineties. I'd expect it to be the most reliable method of receiving messages.

As I said, the general consensus is "take it or leave it" when it comes to demanding reliable banking service. For example, whenever someone complains how angry he is because the internet banking of Bank A was down without advance notice when he had to do a transaction, he would be chided for demanding 100% uptime.

As usual, Malaysians accept poor service and worse, self justify it.

The banking communicates with the telco. Nobody knows what runs behind the scene unless he is in this field.

If Lazada or Shopee or any merchant fails to process your credit card refunds after certain deadline, do you complain to the bank or Lazada?
As a customer of Lazada or Shopee, do you need to know their refund system works?