Is there a way to see if your phones truly unlocked without the PUK code

I bought iPhone off of eBay is the Samsung Galaxy S7 active AT&T unlocked is what it's sad I got the phone I called my Wireless company qlink Wireless and put in the IMEI code they said it was compatible but I needed to have any new SIMs card through them I received that card put it in the phone and tried to activate it by pushing hey ussd code they gave me it did not work I looked up online and found a ussd code for Android phone it did work I don't know what it did but anyway I have 4G LTE mobile network I have three towers on signal call but when I try to make a call it drops down to one bar and it only goes to the darling page and hangs up but never starts ringing I can't receive a phone call I'm really not for sure about text I text someone they never text me back Geico office T-Mobile's Towers so I'm kind of wondering if maybe AT&T my not have unlocked the phone yet all the way