missing apn network settings
i was given a free at&t iphone from a friend. she got it free when her sister signed a contract. she was given 30 days to cancel so she did and had a phone she didnt want. i took the phone to h20 wireless and activated it. i was able to surf the web but i wasnt able to send picture messages to anyone who didnt have an iphone. i couldnt only use imessage for pictures. i stayed with h2o wireless for 2 months. last week i switched to cricket wireless. now i can send picture messages to anyone but i cannot surf the web. i was told to go to the apn setting and set them up but i have no apn settings on my phone at all. under cellular network it says celluar data on and there is no option for he network. there is also no option for the carrier. (right under the cellular) cricket told me to go tot he apple store and the people at the apple store told me to go back to cricket. after some research i see that some sim cards block apn settings. so i'm wondering what i should do now. im very frustrated and im ready to trade in/ sell my phone and switch carriers again. please help. i have ios 9.3.1 and its up to date. i went to unlockit.co.nz and cricket wasnt listed. several at&t options were there but i didnt know if i should pick one and if so which one. someone please help me thanks!
iPhone 5s, iOS 9.3.1