Actually no GST but there is AF from bank, and usually AF is higher than GST, not sure it is a good news.
Cannot la, we are from different industry, different specialization. If I were to use the same method as yours, I will kill myself. People at my age, engineers are already earning 5 figures. So, what's mine? I'm just a HR, so have to be fair when doing benchmark.

Yes, I read about the AF part.
That only needs to be concerned if you don't pay your bill on time.
So long you pay your statement balance as per the date mentioned in your M2U, then there won't be any interest imposed to you.

That means there is no outstanding balance for AmEx?
Check your statement balance?

Statement balance - Pay before your due date
Outstanding balance - Includes your statement balance + unbilled transaction, don't need to pay now until it reflects as statement balance.

I hope the above explains.

That means your AmEx is not linked to your M2U.
You better call CS to clarify further.

Few days ago, one of the forummers also mentioned that there is issue linking his AmEx and still unresolved until today...