depends on if your cohosting or virtual hosting.
for example if you're cohosting i'd change the ip address of the web server and the domain to match. that way if the visitors are bringing up your site by ip or out of date dns entry they won't follow to the new ip. ISPs reuse ip addresses. if your web server is on an ip that was used previously by a popular site then that can drive up your traffic.
if the traffic follows to the new dns then someone is intentionally sending users to your site. does your site have content that users are look to leech from?
start looking for patterns in the source ip & http request headers to see if its a denial of service attack. this is the only case where the police might be used. if users are accidently typing in the url/ip or if someone is sending users to your site you have few legal options.