router and modem issues

ok my isp is charter they are coming out
which if the issue is on their end there's no charge but if the issue is on my end there is
how would i find out where the issue is
when the modem is connected to my pc i get double the dl speed then what i pay for
i pay for 12mb and i am getting max 28mb dl

but when i connect the internet to my xbox one it doesn't seem to pick up the internet what so ever
i had it connected threw my router intill they had issues last nite
when its connected to my router i get 1-3mb dl
but when i have the internet removed from the router i can ftp normal speeds into my xbox so i thinking my router is far from the issue

well it would be f##ked up if they charged me when 2 days ago it worked flawlessly connecting to my xbox and both my pcs threw my router now that they had technical problems in my area it doesnt want to connect threw my router to my main pc and doesn't want to connect straight to my xbox
any ideal on how to really trouble shot this with out them
windows cant figure it out i tried ever thing unplugging rebooting unplugging and at max it worked and i got that 1-3mb dl speed
the make of my modem is webstar and the router is d-link DI-524

Does the pc work

yes but not at the right speeds
i pay for 12mb and im getting double
which is nice but lately for me its not needed and not worth losing connection to my box

does the xbox?

no

over at the xbmc4xbox forum some one said that that setting should connect which it don't thats modem to xbox
here the topic over there
router and modem issues

Add the router, repeat. Does the pc work, and the xbox?

nope sometimes it will but thats when i get the 1-3mb dl speed

D-Link High Speed 2.4GHz (802.11g) Wireless Router
can this router support 20+ dl speeds

wireless signal rate of up to 54Mbp

im thinking so