iphone 7 sim not supported

My name is Joseph Khoury, i bought an iphone 7 when i was in Seekonk from best buy and i made sure with the salesman to have a factory unlocked phone because i live in Lebanon so i paid 849.99$ for that. While my stay in Boston i tried my Lebanese sim card and it didn't work i had a message on the iphone "sim not supported". For that purpose i went for a second visit to best buy and spoke to the customer service to help me with that issue. The answer was that the phone i bought is 100% factory unlocked but the network is not supported in the US so it will definitely work once i come back to lebanon.

I trusted the answer of the customer service person but unfortunately once i arrived to my country the same issue persist.

For that i went to the network company in lebanon to see if the problem is from the sim card but the answer was that the phone is still locked.

Therefor i need from your side to send me the instructions to unlock my phone and to use it properly, it is not acceptable to feel betrayed by buying a phone with wrong settings which i made sure my request was clear " factory unlock"