my isp have provided me static ip
which is used by another person
when he uses i can’t get in
system says ip address conflict

and if i spoof his mac address and then assign the static ip what i get is slowwww internet speed
which is really slow

please guide me and mail me how can i disconnect his pc/router for sometime and let my pc connect with another mac and when again after my connection he tries to get in
system send the same message that system says to me

“ip address conflict another computer on the same network is using same ip address”