Blacklist

I blacklisted my phone after it got ****** and i have been trying to check if the phone is still active after I blacklisted it and the answer I get is I can not be assisted in this matter as they are not responsible for checking blacklisted phones. My question was how do they blacklist a phone and not be able to assist in checking wether my phone is active or not? Please can I get clearity on this matter. Whats the purpose of blacklisting a phone?