I check my modem GUI it gives me a wan ip of 180.xxx.xxx.xxx but if i check on a website whatismyip.com i have an ip address of 120.xxx.xxx.xxx can anyone help?

Use always trustful site for tracking your IP address.

As first your computer have 2 different IP addresses. One is router IP address and you can check it:
http://www.ipaddresslocation.org/router-�/a>
http://www.find-ip-address.org/router-ip�/a>

Another one is your external or WAN IP address::
http://www.ipaddresslocation.org/ip-addr�/a>
http://www.find-ip-address.org/ip-addres�/a>

See what they site above show you and you will know of the site that you have used for testing told you right.

Good luck!

One is your External address given to you by your ISP. The other is Internal given to your computer by your router via DHCP.