I needed to cancel my MobileNet service with AIS. After looking at their 'all style & no substance' website for half an hour or so, I stumbled across an online chat/help facility.

เอไอเอส คอล เซ็นเตอร์

Click on the little moving arrow and a window will open.

It takes a few mins to get going (and to find someone who can write in English), but I got sorted out ok.