Over the last six weeks my prepaid balance has unexpectedly gone down, by small amounts, usually 20c or 40c. I can verify this by taking screen shots from the web portal.

However, when I view my activity in the web portal, there is no activity that should generate charges.

In the most recent case, it went down 40c overnight, and my phone doesn't show any activity, I haven't made any calls or called voice mail. I've sent 6 texts which are shown against my text pack, but I've seen it go down with absolutely zero activity.

My phone is an HTC One, running android 4.4.2. Mobile data is turned off. The data usage app shows zero bytes of data usage during the relevant period, but on occasion Telecom seem to think that I've used some data:



I'm guessing the charges may relate from this, but have a few questions:

1. Why would I  be charged 40c, rather than $1 for 10 MB which is the charge for casual data usage?
2. Is my phone responsible for this, or is telecom measuring this incorrectly?

I'm interested to see if anyone else has noticed this. The total amount isn't enough to contact customer service (about $3 over six weeks), and at this stage I would let it slide, but I really am quite curious as to views as to whether this is the phone using data under the hood when it shouldn't, or whether Telecom is incorrectly charging me.