As @TimothyCole said, they will block traffic to your device. If you didn't see the traffic spike, it wasn't actually attacked.
Also, if you intentionally caused a DDoS to your server, that would put you in direct violation of DigitalOceans ToS.
Section 3.3 section (i):
"3.3 You shall not: (i) take any action that imposes or may impose (as determined by us in our sole discretion) an unreasonable or disproportionately large load on our (or our third party providers’) infrastructure; (ii) interfere or attempt to interfere with the proper working of the Services or any activities conducted on the Services; (iii) bypass, circumvent or attempt to bypass or circumvent any measures we may use to prevent or restrict access to the Services (or other accounts, computer systems or networks connected to the Services); (iv) run any form of auto-responder or “spam” on the Services; (v) use manual or automated software, devices, or other processes to “crawl” or “spider” any page of the Website; (vi) harvest or scrape any Content from the Services; (vii) use the Services for high risk activities including but not limited to the operation of nuclear facilities, air traffic control, life support systems, or any other use where the failure of service could lead to death, personal injury, or environmental damage; or (viii) otherwise take any action in violation of our guidelines and policies."
By your own word, you did just that:
"I've tried to DDoS a VPS in Amsterdam and London with 25 Gbti/s."
Dude, not smart. Just no. Don't do that.