double payment

I have a problem

I firstly use prepaid 40/45 plan. 

Last month, I made a mistake by changing to 25/30 because I still want to use internet data. So, I went to ATT shop. 

The officer helped me changing the plan to 30/35, however,  she made a mistake. My account had not enough to change. So, I went back to the shop again. Another officer helped for several times to fix it. 

Finally, I could use my phone again.

However, I got the message that ATT charge me 44.25 last night. Because I don't want to use 40/45 plan. 

I don't know the reason. 

After going to the shop, I decided to maintain the plan to 25/30.  

Please kindly help me fix the problem.  My phone is *** and please contact me. 

And I have a question about the plan of 25 cents per minute. Does it have any minimum payment per month? If I don't use any call or data or msg, how much I have to pay?

[Edited for privacy-This is a public forum. Please do not post personal or unique information such as but not limited to full names, employee ID numbers, email addresses, phone numbers, account numbers, etc.]