Both letters are headed “Domain Name Available”. The letter from Domain Name Group sells the net.au equivalent of the registrant’s com.au domain name for $245.00 for 2 years. The letter from Domain Register offers to sell the .com equivalent of the registrant’s com.au domain name at a cost of $249.00 for 2 years registration.
These prices are significantly higher than any other domain name registra on the market. You can buy most of these domains for about 1/10th of the cost.
Not only are they completely over priced, but the auDA has received complaints which indicate that either the domain names are being registered with contact details belonging to Domain Name Group or Domain Register, or the registrants are not receiving the promised “free gift”.
There are a lot of these sorts of scams about. They come around in waves from various groups and should always been watched for. You should only ever get emails and contact from either your domain regsitra, or the auDA.