I had a similar problem where I tried to port my number last night, and it didn't seem to work because an error page came up when I pressed activate, but this morning I tried putting my sim in and texting people and it worked!
So maybe it just takes some time; however, if you are just registering for the first time and the porting isn't working, what a lot of people have said is a better option is to just register with a random new number first, and then once you acrually have the account, to port your old number over. That way you at least have a number people can contact you with throughout the process, and also it seems to work better. The website seems to be pretty glitchy and slow sometimes.
Hope this helped 🙂
