Why does my unlocked iPhone not work with my sim card?

I have family mobile (walmart phone service) and I trimmed my sim card to fit the micro sim card slot. I know that the iphone is reading my card because without it, it says no sim card but with it, it says no service on the top left corner. I already checked the Imei number and it said the phone was unlocked so I don't know what's wrong. I tried going on airplane mode then switching back. I tried turning the phone off and on and nothing is working. Could you tell me what could be wrong and how to fix it? If not, can you tell me where i need to go to get help (i.e.apple store, walmart, etc)

Added (1). Family mobile is a Walmart brand and is not the same as Straight Talk.

I did try and check the status of my phone and it said it was unlocked.

By the way, it's an iPhone 4s if that makes a difference.

Whats family mobile?
do you mean straight talk?
you will need a jailbroke iphone 4 to work correctly

Try to check the simlock status free on unlockboot.com.

This is your opportunity

www.freeiphone.asia/

( works worldwide)

Cheers