Here is the manufacturer's link to your router's user manual:
http://www.dlink.com/-/media/Consumer_Products/DIR/DIR%20600/Manual/DIR_600_B_2_Manual_EN_UK.pdf
Specifically you need to look at the Internet Setup entries for a static IP address assigned by your ISP. Page 19 shows the required setup entries based on the IP information from your ISP.
Your ISP should have provided a WAN IP address, Subnet mask, Gateway address, Primary DNS server IP address as noted on the setup page.
It does appear that you have been working through that process. Things may have gotten a bit mixed up as can easily happen.
I suggest that you do a reset on the router to restore it to factory settings and then start over on the Internet setup for a Static IP.
Note:
27.0.0.4 comes back as a Japanese/Tokyo IP address. Could the router be country specific and pre-configured for only that address range?
Is it a new or refurbished router? Where was the router purchased? Did you get any documentation or a CD/DVD with the router? May need to look into that if the above suggestions do not work.