if you get a (small) DDoS attack, you can already block it using iptables (Linux) or the Windows firewall.
If this does not help, please open a support ticket with the following content:
1. since when does the problem occur? It is helpful to specify the exact time and the respective time zone (e.g. UTC).
2. are you still able to login to his server via SSH or RDP?
3. which service/website/destination port is affected?