All the AIS simcards I bought came as AIS Netsim or freedom 3g or whatever.

They have default internet package that bills you 19 baht per week and it can't be cancelled.

We talked to AIS customer service but they can't help, the USSD code they gave us did not worked.

Any ideas how to change promotion of phone back to good old 2baht/0.5 baht there after calls and no internet package whatsoever?

Go visit a Telewiz shop, they can fix it if it is possible.

Strange... They 'should' be able to cancel/reconfigure your package, promotions and Value Added Services over the phone.

If this is on a Smartphone, have you tried downloading the AIS eService application and seeing what trouble you can cause with it?

Have you tried, to cancel the unwanted package through

AIS eService Website?

Sim card is in fixed wireless phone (fixed line phone with sim card - huaweii f111) so I did not have chance to try any application (it is not smartphone).

Anyway I'll try AIS Eservice website as Turkleton suggested.

Edit: After a few tries, I managed to change call plan. Finally!