Problem mapping an existing domain

I am using the free version of WordPress and would like to change my domain address.I have already purchased domain from another company but whenever I try to map it, i get an error message saying: “Sorry but kammerhaaled.ee has not been registered yet therefore cannot be mapped.”
I have also changed the nameservers for wordpress one’s(ns1.wordpress.com etc). Even when I try to search my domain name on who.is(https://www.who.is/whois/kammerhaaled.ee)it says that my nameservers are wordpress one’s. So what could be the problem?