This is the way I see this situation
As Christians, we are spiritual beings and we must treat most situation as spiritual.
The Bible does say that:
The world is unprincipled. It’s dog-eat-dog out there! The world doesn’t fight fair. But we don’t live or fight our battles that way—never have and never will. The tools of our trade aren’t for marketing or manipulation, but they are for demolishing that entire massively corrupt culture. We use our powerful God-tools for smashing warped philosophies, tearing down barriers erected against the truth of God, fitting every loose thought and emotion and impulse into the structure of life shaped by Christ. Our tools are ready at hand for clearing the ground of every obstruction and building lives of obedience into maturity.
2 Corinthians 10:1-6 (The Message (MSG))
When you become a Christian, you must behave Christ like because everything in you has been made new. Christ never said anything He never meant, His yea was his yea, and his nay was his nay just as we Christians are encouraged to do so as well.
Our tongue is very powerful but there is more to it once you become a Christian as well. We must be aware of what we say about ourselves because most things we say and do are sanctioned in heaven. We must understand that everything in this world is controlled by heaven and our lives is not excluded.
If somebody pronounces evil against you based on the assumption that if God does not answer, other forces will answer, then there are at least two things, I will suggest to counteract the negative pronouncements.
The Bible says that those who know their God shall do exploits, If you know your God whom you serve, If you follow your God in all righteousness and you strongly put your faith and hope in Him, then by all means, run back to Him and present your case before Him, He is bound to answer back the enemy from heaven. He did it so many times in the Bible - Hezekiah was plagued by the king of Assyria, he cried out to God and He answered him.
Secondly, I would say, reject it straight away. Tell the person, I reject your evil pronouncements, the bible say that there is no divination against Jacob, neither is there any enchantment against Israel. As a child of God, you share in the blessings of Abraham and whosoever bless you will be blessed, whosoever curse you will be cursed. Confess the word of God over your life and leave the battle to God to fight for you.
I don't want to say too much but I hope this helps.