If you have registered an international domain name (.com .org .net etc.) there is a good chance that you have either received or will receive a letter in the mail from a company calling themselves Domain Renewal Group (or Domain Registry of America). It is scam - my advice: trash the letters from Domain Renewal Group out - they are only trying to steal your money.
Note that the letter looks very formally. They state in the letter that your domain will expire soon and you will need to act today.
If you receive such a letter, you just throw it in the trash, do not pay. It is a scam company and the money you pay disappears without renewing your domain.
The right way to pay for renewal of your domains is to pay them via your regular domain registrar.