I thought I had done the I noticed another similar post and followed the instructions, I've changed the IP but its still using the original IP. I assume the the ISPConfig server needs to be the DSN server?
You have to change the IP address in the DNS server that is authoritive for this domain, this can be your ispconfig server but it can also be a different DNS server. You can find the authoritive dns server for a domain with: dig NS domain.tld