Carrier lock shows sim locked

I have not purchased a carrier locked device . I purchased iPhone 2yrs ago from apple store which is unlocked version of the phone by paying full amount. Now I’m traveling to india . When I tried to use my india sim I noticed carrier lock shows sim locked. I contacted my carrier they say they have to capability to lock or unlock the phone as they sell only prepaid sim. I’m struggling with this issue . Someone please help me to solve this issue.