visual studio 2017 stuck building ue4

I saw it needs .NET Framework 4.6.2 - so I downloaded and installed that – well I tried to anyway. When I did so the installer said:

.NET Framework 4.6.2 or a later update is already installed on this computer.

so Windows thinks .NET framework 4.6.2 is already installed, but Unreal thinks it’s not. What do I do now?