Very long story ahead!

Yesterday in the evening a friend of mine (calling him F from now on) became the target of something new to me...
Apparently one can fake his phone number through some fishy ways and call people with that number. Someone (we think we might know who it was, the why is at the end) did this yesterday to F.
Here's the whole story:
We were just talking together on a TeamSpeak Server (a program to talk to others on the internet) when suddenly another friend said: "F, why did you just call me three times in a row?" That was the first thing that was a bit suspicious. After that, F got calls from random numbers (even Afghanistan, we are German), and they said something like "Have fun with the police coming to your house". Then there was silence. 10 minutes later his phone rang and there were a ton of pizza delivery services in his town that apparently got pizza orders from him. Then there was silence, again. Suddenly someone with a hidden number called him, a woman's voice said they were the police and if F doesn't stop calling the police there will be consequences. F then told her what was going on but I think she didn't really care. She then wanted to know where F lives, but I told him not to say that, because if it is the police they can find it out by themself and if it's not, they don't need to know that.
Now, a short break: There is some fake information going around about where F lives. I can't remember when we found out but the attacker thought he would actually live there. No idea what happened at that location...
Now back to the story:
Time went by, nothing really happened. Suddenly F shouted: "There are blue lights outside! The police is here!" He muted his microphone and (the following is what he told us what happened) went down to the door (remember, he is 16) and there were two police men. They were asking about why he called the police. F explained what we knew until then, about number spoofing and stuff... They sent a more technical person to him, he understood what F was trying to explain. The police men drove away and he came back to tell us what happened. (Now we get back to what I heared myself.) The mom came in, screamed something that I couldn't understand, and F went offline. We searched who the attacker could have been. And we are pretty sure we found him. That guy connected to our Minecraft server (that's where I know F from) with his real IP, and his main account, which made it easy to search. He also got a static IP which means it doesn't change. We also got some information that in the recent days this guy was talking about VoIP spoofing and such stuff. Another friend of mine, a bit older, found some proofs and I think he will go to the police.

That's it. Thanks for reading.

TL; DR: Bringing up quantum computing is going to be the next catchall for everything and I'm already fucking sick of it.

Actual convo i had:

"You should really secure your AWS instance."

"Isnt my SSH key alone a good enough barrier?"

"There are hundreds of thousands of incidents where people either get hacked or commit it to github."

"Well i wont"

"Just start using IP/CIDR based filtering, or i will take your instance down."

"But SSH keys are going to be useless in a couple years due to QUANTUM FUCKING COMPUTING, so why wouldnt IP spoofing get even better?"

"Listen motherfucker, i may actually kill you, because today i dont have time for this. The whole point of IP-based security is that you cant look on Shodan for machines with open SSH ports. You want to talk about quantum computing??!! Lets fucking roll motherfucker. I dont think it will be in the next thousand years that we will even come close to fault-tolerant quantum computing.

And even if it did, there have been vulnerabilities in SSH before. How often do you update your instance? I can see the uptime is 395 days, so probably not fucking often! I bet you "dont have anything important anyways" on there! No stored passwords, no stored keys, no nothing, right (she absolutely did)? If you actually think I'm going to back down on this when i sit in the same room as the dude with the root keys to our account, you can kindly take your keyboard and shove it up your ass.

Christ, I bet that the reason you like quantum computing so much is because then you'll be able to get your deepfakes of miley cyrus easier you perv."

Either CloudFlare itself has decided to join the fun of attacking my DNS server, or somebody is just spoofing their IP in the UDP packets.
Crap, my ipset script is basically useless now, since the real source could be from anywhere :(

Any suggestions on what could I do to make this attack stop? It's not causing any real issues (at least for now), but it's still annoying as hell.
Get fucked, stupid skiddie who keeps manually changing the ip source in his script

How do you prevent your software being vulnerable to IP address spoofing? Authentication? Certificates? VPN? Nah, just check the MAC address field of every packet. Nobody ever spoofed a MAC address before, that's just impossible. I thought that in binary there were only ones and zeros, but I guess nobody told me about the special tamper-resistant ones and zeros that MAC address fields are made of.

Oh, once you've done that, don't forget to tell the marketing people to put it in a brochure as an "innovation" for everyone to see.

I should post more of the crap the idiots I work "with" (quotes, because I am only here in body not mind) say. Especially when it comes to network stuff.