Could not activate iPhone?

I'm using my phone from 1year. I bought it from someone who used to live in USA. He brought the phone with him & sold it to me. Before buying the phone I did a full reset to wipe out all previous data. then I put my own apple id. 2weeks ago I thought to hand over the phone to my son as his phone was lost in a concert. I tried to reset my phone before I give it to him. But after the reset my phone is not activating. It's showing this dialogues. It's been passed 2weeks but no response & I & my son both are stuck. followed all the rules as described in apple support.

I have already installed the sim I used. Now how can I get rid ou of it. I'm from Bangladesh & there is no nearby or any customer care of apple in my country.