Hi,
The thing I guess you are facing is Denial of Service Attack or DDoS Attack. Generally, it is performed by competitors to make a bad impression about your products online.
The terminology is not as simple as it looks like.
Before taking steps, I need to see the logs of your server. Both Http/Https/FTP,. Though HTTP / HTTPS will be enough. I'll need also server info like I/O, bandwidth, hosting provider etc.
I'm open to any kind of discussion. Don't hesitate to knock me :)
Regards
Delowar