Wired: No valid ip configuration, sudden loss of internet

Hey! After trying my very best to solve my brothers issue with wired internet connection my progress has came to a halt, so i need your help.
I'll do my best to translate and be specific, but please tell me if you need more info and I will answer asap.

TLDR: Randomly lost connection, gets error no valid ip configuration, tried lost of solutions, still no internet and 12gb gone from his phones dataplan.

Let's start at the beginning.

Brother moved for college in August, been set up with everything working nicely. Has separate output for wired internett connection (via modem), has no wifi and prefers wired connection.

Issue hit him after visiting parents one weekend. Random loss of internet connection, and total internet blackout. This goes for 2 different laptops and his PS4 aswell, which i find very weird. Managed to fix the problem (weirdly) for a couple of hours 1 day later on his laptop, then no connection at all.

Currently lives in a house split into different apartments, same internet line and provider, everyone else has internet (both wired and wireless.)
Not sure how many others share the same line, but has worked excelently until this point.

Wifi WORKS from his phone.

PC speccs: PC - Windows 10 Home x64 system Model = ASUS ROG G751JT (17 inch) Windows version = Windows 10 version 1607 Network adapter wifi = Intel Dual Band Wireless- AC7260 Network adapter Ethernet = Realtek PCIe GBE Family Controller Previous Antivirus = McAfee Current Antivirus = Windows Defender (post format)

Error messages:

CMD>ipconfig:

Ethernet adapter Ethernet:

Connection-specific DNS Suffix . : Autoconfiguration IPv4 Address. . : 169.254.xxx.xxx Subnet Mask . . . . . . . . . . . : 255.255.0.0 Default Gateway . . . . . . . . . :

Tunnel adapter isatap.{69E8DE53-419F-45BD-AF3D-xxxxxxxxxxxx}:

Media State . . . . . . . . . . . : Media disconnected Connection-specific DNS Suffix . :

CMD> Ipconfig /release + Renew

Release: An error occurred while releasing interface Ethernet : still no adress connected to network-connection point (translated)

Renew: No reaction, Timed out after about 5min.

Windows Troubleshooting = Ethernet has no valid ip configuration

Cronological troubleshooting.

1) Randomly lost connection
2) Booted both pc and router
3) Checked cable for errors, and bought new.
4) Manually setting ip/gateway/dns
5) Tried most relevant netsh commands through CMD(admin rights) netsh INT IP reset/Netsh winsock catalog reset etc. and booting laptop inbetween.
6) Checked networkcard drivers (up to date)
7) Rolled back drivers.
8) Clean reset of ALL networkcards
9) Deinstalled ethernet card (multiple times)
10) Deinstalled Mcafee.
11) unplug cable, reboot, plug back in, set automatic ip, set pc as visible on network. BOOM internet for 4-5 hours before loosing it.
12) Steps 1-11
13) Complete format of laptop
14) Update windows and network drivers.
15) tried CMD>PING modem ip >gets response 4/4packets
16) tried CMD>PING google ip >no response
17) tried CMD>PING google ip >1/4 packets(from modem only)

- Tried googling all possible varieties of gives problem and look for solutions(those above) and has found nothing that works.
- Tried connecting in neighbours working router

Has also called network provider support, they seemed to not know what they were doing and could not provide any solutions to the issue at hand, but will try them again later this week. -Support guy said he could not see the laptop connected to the modem.

Also has plans to buy a router with wifi to see if this solves the issue. (tomorrow)

The weirdest thing here is that he lost connection on multiple devices simultaniously who had all previously worked fine, and is still not working on his output or the neighbours.

ANY ideas to solves this issue would be MUCH appreciated as he is currently eating up his phones dataplan (expensive) and has exams coming up in not too long.