A common scam at the moment is for domain name companies to send you "invitations" to renew your domain name through them. This would normally be fine, except that the renewal is made out to look like an invoice.
One serial offender is a company called Domain Register Pty Ltd (also sending out notices under the name of Domain Name Group Pty Ltd and Domain Renewal Group Pty Ltd). They send letters to people, made out to look like invoices, but if you check carefully, it is normally for a domain name you don't even own. The idea is to trick you into thinking that it is an Invoice, and unfortunately many people are falling for it.
As if that wasn't bad enough, the prices they are charging for .com domains are around 500% higher than current market value!
What should you do if you get one of these letters? Just throw it in the bin. If your domain is registered through Domain Hosting Shop, your renewal notices will always come via email from service@domainhostingshop.com.au, and will have the Domain Hosting Shop logo on them.
UPDATE - these "Invoices" are now also arriving under the name of Name Juice Pty Ltd and The Domain Registry of America. This appears to be the same scam.