I'm sorry to hear you are having issues downloading the modpack. Fortunately for you, there are other options available to join the server. I would recommend downloading Forge 1.12.2 manually and then adding the mod to your mods folder, which can be found here. If you are on Windows, you can press the windows button and R at the same time, type %appdata%, click .minecraft, and drag the mod into the mods folder. For Mac, open Finder, go to go, library, go to application support, Minecraft, and drag the mod into the mods folder. I hope this information is helpful to you, have a great day!