My Family Mobile Walmart phone plan Billing for services not used Internet

I went to my local Walmart store and bought the Sim card for around $25.00. They said that it was month by month and that if i didn't pay each month my phone would just automatically shut off the service until I paid the bill. I thought HEY! that's a great deal only 35-40$ a month! 

To make this story a little short, I am VERY disappointed in Family Mobile, when I had first got the service about a week later I went to WI with one of my friends, there was barely any service there, the only place i would get service is by the lake. Which was horrible when I was trying to get a hold of my parents when I got an ear infection and had no service!

When I came home the next day I decided I didn't want the service and cancelled it, SO I THOUGHT! I got the actual T-Mobile plan connected to my parents account. Well 2-3 months later I get a bill for $78.65! They were charging me for services I didn't even use! Keep in mind this is a MONTH-BY-MONTH phone service! I called and they had said that I have to pay the bill and that this wasn't a pre-paid service? then why did my local Walmart store tell me that it was?... They wont take off the months that they obviously see that I didn't use the service! Why should I have to pay a bill for one , if i didn't use the services, and two, if i'm not even under a contract?! They say that I receive the bill by text, well how am i suppose to get a text? when I'M NOT USING THE SIM CARD!  , well they're a paperless company. HOW IS THAT MY FAULT?! But you sure do send a bill in the mail when it's $80.00!  I wouldn't recommend this phone plan at all its a RIPOFF! and they're VERY UNORGANIZED!