Unlocked iPhone

I need your help with my Walmart’s purchase. It was an iPhone XR, before I bought it I asked them if it was unlocked and they told me it is. But after four months when I tried to use another provider it doesn’t allowed me. than I contacted Walmart and they said after 27 hours it will be unlocked. Than 27 bass no change happen. Honestly,I am so frustrated. I contacted Walmart again and they suggest me to contact with Apple support. I need to find a solution to this problem can you help me with this.