This is an Android phone which means that you can use a security solution available for cases like these. Download any of the items available and perform a scan of your phone then you should observe its behavior regarding SMS, calls, current cost, Internet traffic. Sometimes these are pretty obvious and it's easy to identify if there is something installed in your phone due to large amount of data being transferred, over excessive cost control, etc. I recommend on doing a factory reset which will wipe all the settings and return your phone to its factory state.
