Some things to consider:
- How hard is it to give your villains a new name and 'find and replace' it?
If it isn't hard to change, the politician is still alive, and you don't want to cause them or their family any harm or bring your readers any confusion, it may make the most sense to just change their name.
- How common is the politician's name?
Paul Ryan is an American politician, but if there were two evil twins named Paul and Ryan in a story I probably wouldn't connect them with him. Jokong appears to be the name of a town in South Africa and I can find about 5 pages of facebook profiles that could possibly go by the nickname 'Jo' Kong.
- How similar is the politician to your character?
Same gender? Race? Nationality? Do they both have ridiculous mustaches? If Paula Ryan is a petite percussionist who grew up in South Korea, I'm not going to connect her to the American speaker of the house and he shouldn't have much cause to complain when Paula is revealed as evil. If Winston is rather stout with an ever present cigar, however, people may start drawing certain connections.
- How likely is it that your readers will know of this politician?
You mentioned you haven't heard of this person. Is it because you're young, they're relatively obscure, or some other reason? Is there a chance you heard of them before and subconsciously applied their name to the character? The US has 435 house representatives, but most Americans probably wouldn't recognize more than a handful of names. Coming across a character who shares a name with my house representative would be about as weird as a character who shares a name with the kid who sat behind me in math class--disconcerting, because I already have a mental picture of that person, but only about 0.25% of the US would have the same response.
- How realistic is your story?
Is there magic in the air and dinosaurs roaming the streets? Or is it tucked back in a plausible sounding town in the modern era? In the US at least, something that's obviously fiction is treated with more leeway than a memoir.
- Are you self publishing or working through a publishing house or distributor?
If you're publishing through someone else it is very likely they will have their own opinions/policy regarding this issue. At the very least they will likely have additional experience to advise you.
- What are the libel laws like in your country and the former
In the US politicians as public figures have more limited protections, but they do have some. There're also laws preventing 'libel tourism' or people going to other countries where the laws favor them and suing from there. I am not a lawyer in the US or any other country, but if you're in doubt and ready to publish it may be worth consulting with one.