Error when creating page

Hello,

I’m very new to wordpress and still trying to get my head around it.
I’ve installed the mistercorporate theme but when I try to create a page, insetad of displaying my content it just shows
“Contact us!
Mr.Corporate.
An elegant corporate theme by Ns themes”.

What it is really odd is that it keeps displaying it even if I choose a different theme.
This is preventing me from publishing any content on my website.
Anyone has any ideas why this might be happening?
Thanks.