how can i defend myself against the DDoS attack

would you like to try HyperFilter for this, but their price is much around 300EURO a month, for such protected HPS.

There is not much you can do on your own, you'll need to employ a service or a front-end with a DDoS Filtered IP. You can run a GRE tunnel from that endpoint to whatever you are trying to protect. Another option would be to just host on something that is DDoS Protected already, or get a VPS and get an additional DDoS Filtered IP.