Unfortunately you will need someone with physical access to do it*; they can boot into single user mode and make the required change. I assume that you are renting a server? If so then you will need to make it really simple for your ISP's technician, something like:
1. Boot into single user mode (This is my root password) 2. Delete /etc/deny.hosts 3. Reboot server
Best to have them delete the whole configuration, rather than try to get it edited. Much better chance of it working first time and keeping your bill down.
* If it is just YOUR IP that is denied... go and use someone else's connection... a friend, or the IP at an internet cafe (just change your PW when you get home)