Newbie questions why i always fail, need to buy egiftcards with cvv

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#1
I change my location to cc holders area, clear cache in firefox and make sure timezone matches n everything is green (no blacklist ips, dns leaks) on check2ip.com. but my cards keep getting declined. Am i doing anything wrong or its the cvvs? Can pros please help me im down to split whatever to learn my errors pls help