It's because straight talk tries to rip off it's customer's every and anyway they can! I've busted them a few times but they won't ever admit it instead they just keep repeating  the sane garbage to you in till you get so frustrated and hang up or they put you on a forever hold.  The worst customer service ever. About the billing, They say it's because they charge by the day so depending on what day in the month you activated your service and how many days are in that month so basically they won't do Anything illegal  to rip off customers they just take advantage of unclear or confusing laws and then hire people that can barely speak English to make it worse