I checked your website but as soon as I enter it, it goes into an infinite redirect loop. The main page of your site seems to contain a HTML redirect, but the URL is incorrect and results in the page just redirecting to the main page again, triggering the infinite loop.
I think that this problem is caused by a syntax error in the HTML redirect. That said, I would recommend switching to a PHP redirect instead, then you get a proper HTTP redirect instead of a HTML trick.
When I try to visit the page the HTML redirect is supposed to redirect people to (http://celis-molotla-eduardo.infinityfreeapp.com/EncuestaDef.php), I see a 500 Internal Server Error, suggesting that the PHP code crashed: Http error 500
So I’m unable to find the 502 Bad Gateway error. However, I know that that error can be caused by bad code too. Given that there are two other issues preventing me from seeing that error in the first place, I suspect that the 502 error may also be caused by a problem with your code.