I'll do half-a-reply since nobody else has bitten.

Only once did I personally do a bank transfer. It was GBP from the UK to a Vietcombank account in Hanoi. It arrived next day without a hitch.

I know others who do transfers to/from Vietcombank without any issues - usually USD from the UK.

I believe Vietcombank are pretty efficient - I'm guessing the problem is with Saigontourist. I doubt whether there is any overt dishonesty on their part - but they are not the most responsive of organisations.

If its a telex transfer, there is a way to trace the payment. My own bank charges for this - the fee is the same as for the original transfer, though I suppose they would refund if they were in error.

By the way, I'm not sure how common it is for full payment to be insisted upon prior to arrival. (I can imagine state-run Saigontourist might be the least flexible). Some VN-based private tour companies require only a deposit and the balance payable on the first day.