Apple Iphone 5s In Usa Unlocked

I did purchase a fully unlocked iPhone through Amazon, in which I shipped it to Costa Rica. Once here I get signal but I am not able to activate it since I get an error message that says SIM not supported. I reach out to apple and they stated that it was unlocked but since it's sold by a 3rd party, is only unlocked for the US Market. Can it be unlocked? Do you know any constraints in which sometimes it's only locked for worldwide and unlocked only for US?

Shop for apple iphone unlocked at Best Buy. Verizon Lg Flip Phone Unlock Code. Find low everyday prices and buy online for delivery or in-store pick-up. Shop Apple iPhone® 5s 16GB Unlocked GSM Smartphone 7502427, read customer reviews and more at HSN. Amazon Iphone 5s Verizon Unlocked more. com.