Call into T-mobile or message them on Facebook/Twitter. The reps will be able to look at your account and answer all of your questions. This forum is public thus this kind of info is not really recommended to be discussed in my humble opinion. That being said the small charge is probably some form of local tax or fee that T-mobile has the customer pay.
1 (877) 453-1304 here is there support number but you can also just dial 611 on your device.
Manage your T-Mobile account