Can't replace old website for new WordPress website

Pleeeease I ask for your help, cause I’m a newbie here and I invested a lot of time creating my new website with wordpress, and now I’m clueless :/

I’m trying to replace an existing website https://www.kangtai.cl (not wordpress, made by a friend) e for a new website I created in WordPress.

I proceeded like it was suggested in several support threads in the forum:

1) I created a subdirectory in the root directory which I called “temp”
2) I installed WordPress at a temporary address https://www.kangtai.cl/temp in the same host of the old website
3) I built the new website https://www.kangtai.cl/temp using wordpress which it looked all good.
4) When I was ready with the new website, I moved all the html and php files and some other directories that were in the root directory to a folder I created named “old_site” using FTP (filezilla)
5) I changed the site in the box for WordPress address (URI) and the Site address (URL) from https://kangtai.cl/temp to https://kangtai.cl
6) I moved all the wordpress files and directories from the subdirectory “temp” to the root folder “public_html”, using FTP
7) I deleted the “temp” folder

And when I finally thought I was all set, it came the problems. Now, when I use the URL it sends me to the same old address https://www.kangtai.cl/Welcome.html that it used to upload before ( I have no clue where it gets the /Welcome.html), with the difference that instead of loading the old page it throws an error. However, what I expect to see when I use https://kangtai.cl/ is the website that I created in WordPress!!!