Sudden Bill Jump

FYI, I am very cautious about my phone bill. I checked it every time i can. By pressing *128*1*1# call.

I thought that the cutoff date for Digi is every 16th of the month. I kept checking so i know that i have:-
Outstanding Bill RM0.00
Unbilled Amount RM53.0+

So since i am still within that RM58/ month range i am still ok with it.

Yesterday, i was whatsapping with G in Perth while waiting for my turn/ chance of watching So You Think You Can Dance (SYTYCD). Again it is free texting with this app. After a while, we stopped and i watched youtube through my iphone. I kept receiving text from Digi saying that i have exceeded the 1G  plan. But again data plan is unlimited even after i exceeded the 1G plan. The shocking thing was, when i straightaway check the bill again, it shows that:-

Outstanding Bill RM83.56
Unbilled Amount RM9.00

Then i check my OCS Bill Summary- It was stated that the RM83.56 payment due date is 16th of May 2011.

Another one in the Unbilled Transaction shows:-

Unbilled RM43.40
Total Outstanding RM43.40

Then what should i pay on the 16th of April?

Haiya.. Bingung o sia..~ why bring forward the April bill to May? Is the RM43.40 my April bill?