First off, may I askwhat phone you are using? Since you mentioned that you subscribe to Unli-Surf, I would take it that it's either an iOS or Android Smartphone.
If I am correct, then let's proceed to get a grasp on the issue here. Data charges are incurred when - and only when - a session is triggered from a SIM. This is for certain since each session is captured by various network elements before it is allowed to transfer and receive data. Basically, your phone is it's own modem, and it authenticates itself befofe it gets permission to connect to the net.
Now, unlike the earlier generation of Internet capable handsets where a user has to purposely make an attempt to access specific info before a data session is generated, today's Smartphones don't quite behave the same way. You see, they were designed to be always connected to the net - pulling and feeding information to the user - at every given turn. This means that whether or not you ask it to, it will conduct a session of it's own, and this happens for many reasons. A few examples are:
1) To check for updates on installed Apps.
2) To pull new email from a server (if configured)
3) To check for new versions of the OS (specially for Apple handsets)
Here's a little more helpful info that's not readily shared by the manufacturers. For certain Smartphone models, even when you set the data connection of the phone to "OFF", it will only prevent online activity for third party software or apps. It will not restrict itself to check for OS updates every so often.
So once your phone is properly configured to access the web, it will utilize that capability for housekeeping purposes, if you will, and make sure that the handset is always functioning well. And for those who do not have an active unli-surf service and are configured to TIME or 5 pesos for 15 minutes - then each attempt that the phone does without your knowledge will cost 5 bucks. You being configured to Kb - gets charged by the kilobyte.
To prevent this from happening you can choose between 1 of 2 options:
a) make sure that you are connected to a wifi hotspot whenever possible. the wi-fi connection will always supercede the 3G / LTE service and use that to pull or push data.
b) set your APN config to not be able to function properly. This is done simply by adding an additional character to the APN. (if you want to use data again, just simply remove the inappropriate character from the url)
Hope you could give these suggestions a try and see if you still end up incurring unwanted Data charges.
The new features and functions of Smartphones are more complex than just being able to do immediate email or do facebook on demand and even play games with friends remotely. So don't let your Smartphone outsmart you.
Let me know if this helps! Thanks!