Family Mobile Walmart Family Mobile Keeps charging a customer after they have already ported there number when its a pre payed service. Nationwide

So I called Walmart Family Mobile on Febuary 4th 2015 and got my phone number ported to a diffrent cumpany. I also told them that I would not be using there service any more. In the months to fallow they have still been charging me for there service that im not using. This is a pre payed service not a billing service. It is alegal for them to keep charging me for there phone service that i do not have. 

This is fraud activity.The lady told me on the phone that i still have to pay for my service. Hello I ported the number to a diffrent cumpany I dont have service from them at that pointl. But yet they still think thay can charge me on a pre payed phone that has no number. ya ok fraud.... Now they are thretining to put these charges on my credit. THIS IS A PRE PAYED PHONE....... You can not do this. So this is a rip off..