Constant disconnects, playing online impossible

I've got a huge problem with my Dark Souls 2 SOTFS PC version. It is impossible for me to play online. I get disconnected quite often, but it's always different. Sometimes I get disconnected every 10 minutes, yesterday I was was online for hours and I got disconnected when I tried to summon somebody.
Summoning doesn't work in 99% of all cases for various reasons and as I already mentioned I also get disconnected quite often when I try to summon somebody. Some rare times when summoning worked (in this example before the pursuer's boss fight) I could interact with the phantom(s), they used emotes etc. but when I entered the boss room they didn't come in through the mist and when I died I did not respawn or anything. I, as a non-present spectator, stayed in the boss room and saw the boss go back to its initial position and could only move the camera and watch. Only killing the task and restarting got me out of that. And this strange phenomenon occured every single time I succeeded in summoning someone (and died).
Another weird thing is when I try to make bell keeper PvP (at Belfry Luna). If I use my ring and invade others as a grey phantom (in case this works at all and I'm not disconnected before or while waiting) it's extremely laggy and by extremely I mean that I can backstab or hit the host and he doesn't lose any TP. And in the next moment, when he's at the other end of the room, I get backstabbed by him and suddenly teleport to him. It's not possible to fight this way.
I also tried helping as a white phantom. There it is the case that I don't deal damage to anything and I mostly get kicked by the host as I don't know what the hell's going on. From his point of view I'm probably hitting the air or anything.
My internet connection is great, it works perfectly fine in every other game and everything else so that cannot be the problem. I can also paste a speedtest later if anybody wants proof. Opening the ports didn't change a thing. I also already had huge connectivity issues in DS. I don't know what to do anymore, I really want to do PvP and help others or sometimes get help from others. And I don't want to get disconnected over and over again. I'm sorry about the wall of text, but I feel like it is necessary to explain my problem as detailled as possible.
I hope someone can help me, I'm going crazy over this.
EDIT: Retried Port Forwarding, did not fix anything again.
Best Answer
It seems like you're losing packets here, but I would suggest that you try port forwarding anyway. You can find referenced guides here and here.
If you don't know how to do that, what you want to do is go to Portforward.com then find your router. There will be an ad, but you can close it in the top right corner. You can probably just use the default config using the link found in the top paragraph of the page, generically seen below
If you do not see the program you are forwarding ports for, you can try checking out our Default Guide for this router, which is a generic guide that should help you get through the basics of getting an open port on your X
Then you want to follow the instructions for that specific router to allow the following ports:
UDP 27000 to 27030 TCP 27014 to 27050 UDP 3478 to 3479 UDP 4379 to 4380 TCP 3478 to 3480 TCP 5223 TCP 8080 TCP 50000 to 50100 UDP 50000 to 50100 UDP 3458
Once all of these ports have been forwarded, you should notice an improvement in connection quality with other Dark Souls 2 players. If not, you could also try the more complete list of ports in the original posts of either link at the top of my answer.
Pictures about "Constant disconnects, playing online impossible"



Why do I keep getting disconnected from online?
If you're too far from your router, your internet may cut in and out as Wi-Fi signals struggle to reach your device. Obstructions between your device and your router may also cause intermittent disconnections. Pay attention to your device's Wi-Fi signal meter to see where your Wi-Fi signal gets weak and disconnects.How do I fix disconnecting constantly?
Quick fix for the "Internet randomly disconnects" errorinternet dropping out solved!! issue with online gaming?
More answers regarding constant disconnects, playing online impossible
Answer 2
This is a tough case, because the symptoms do not point to one cause.
For starters, you want to rule out any of your equipment causing problems. You want to setup a "direct" internet connection. If possible, direct from modem to computer is the best, but almost no providers do this anymore.
Next best is to set up your computer as the "DMZ" target. This basically means anything pointed to your external IP goes to your computer. Do NOT leave your router in this mode, because your computer will probably get hacked.
If this "solves" the problem, great. The problem is with your equipment. You can at least fix it.
If the problem persists, then the problem is beyond your network. You'll have to call your ISP and... well, quite frankly YMMV by a LOT at this point.
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Julia M Cameron, Julia M Cameron, Yan Krukov, Julia M Cameron