I wasn’t thinking about a break in your equipment, or between your equipment and your Internet Service Provider… but between your provider and the EU server for Diablo II. For example it could be a bad relaying server. Testing a different source is a way to quickly check for that.
In other games, a VPN can be used to check for that… but Diablo II does not allow VPNs… so one has to try something else.
The last time we had that trouble… a month or so ago, Blizzard had to step in and fix the issue… see Diablo 2 legacy uswest cant create games for details. Unlike the last time, you seem to be the only one facing this issue… thus my suggestion to use another source for internet… such as a hotspot on your cell phone – ensure that your cell phone is not connected to your home Wi-Fi, but is using the cell phone data plan instead.