security > dmz > fill the wan ip of pfsense

i now have speedtouch i did the followings trying to be able to access my pfsense box from wan:

network > devices > assin the public ip address of a connection to a device > select the pfsense box.

on the pfsense box i did the follwoings:

interfaces > wan > type = dhcp

result:
1-i am not able to access the internet as client
2- pfsense box cant see the packages to download

even if i try to get the private ip from speedtouch via dhcp pfsense cant see the internet
but if i punch in the ip as fix ip, every thing works fine.

any boy having speed touch managed to fix this issue?

thanks in advance

hadi57