I have a server that is under a huge SYN attack. I keep blocking off the IP addresses that are attacking me, and the next second new IPs keep attacking me again, my firewall keeps banning them every minute but then it comes back.
Depending on the size of the attack (and if they are spoofing) really there's not much you can do to stop the attack other than to simply "deal" with it. If they are hitting a PHP page you may try converting it over to static content until the attack is over to lessen the load on the server and you may want to optimize the site to use as little bandwidth as possible.
If this is the case then you will need to contact to the hosting provider and the tech support engineers working there , they will need to block the traffic from high end. They must be able to help you out with that.