You're paranoid. Real stalkers or bots won't create accounts using same IP address.
Method 1
Even if they're dumb as hell, if their provider uses DHCP, one can just hard reboot router and bam new IP.
Method 2
If no DHCP, one can clone PC MAC address to Router MAC Address to change IP address as well.
Method 3
Even if you cannot do any of the above, then you can just run VPN and boom new IP.
Method 4
Even if you do nothing, every 30 days or so, most providers run a clear cache/reboot procedure, so it'll provide you with a new, but similar IP address.
The people caught with same IP addresses aren't the ones you have to worry about, they're noobs.