As mentioned this would be a way to test the network.
We are not advertising anything, as we actually lose money on every sale with that promotion code (you can confirm this by contacting DTAC about wholesale price for SIM cards, and you would see that you are getting a better rate than even that).
It was merely a $5 suggestion on how you can easily test another network without going to a shop or signing up for a contract or monthly plan. This may help someone else which is in another province having similar issues as yourself.
We did not know your past experience with DTAC, and wanted to correct our original post.