So I created a new netflix account and I put my credit card details as the payment method( i tried paypal but it detected that i wasn't from usa).

Anyway,everything went on fine and my trial started.But when I go to my account i see: "No payment info"

So I added my credit card details again,it doesn't give any errors,but when i get back to my account again it says no payment info!

Then,I changed the vpn,so i got to the netflix UK.Surprise! My payment details appear fine under my account!

I must say that I first registered on the netflix USA and not on the netflix UK website!

I don't understand,what could be the problem?!

Call Netflix.

Dunno what went wrong, but I wonder why you didn't just register on your local Netflix site (assuming you have one), or another than US (since they are special), then just use VPN or even cheaper/easier: use something like hola.org to access US Netflix repo.