Wont let me buy?

I try to purchase rust and stuff but this error always comes up when i try to: An unexpected error has occurred. Your purchase has not been completed.
Please contact Steam Support.

Maybe you should contact steam support.

Try logging in on the website with this URL to force the US store: https://store.steampowered.com/?cc=US

There’s nothing strange about that link, it’s just the normal Steam Store URL with a switch manually setting the store to US payment options. This is useful for situations such as if you were, for example, on vacation in Canada. The store would preset itself to Canadian payment settings based on your IP being temporarily in Canada on your visit, and your US Steam account would run into this error because it doesn’t have a Canadian billing address. ?cc=us manually overrides region guessing.

Why this would affect your Steam account, no clue, and no, I’m not accusing you of running Steam through a proxy either. (Although if you were to do that, that could run into the same problem.)

But, yes, contact Steam Support, they’re the only ones that’ll be able to tell you what’s actually going on.

Re install after fully wiping your old steam files

This should work, I have to do it this way when i need to add credit to my account