If it's the internal (LAN) IP changing (which should be outside of the ISPs control), then set the camera up to have a static IP instead of using a dynamic one handled by DHCP.
If it's your WAN (public) address that's changing, sign up for a Dynamic DNS (DDNS) service like No-ip, or DynDNs or alike, and start using the host/domain name they provide you instead of your public IP address.