Hmmm. Interesting. Can you have a look in the C:\Users\<myUsername>\.platformio\penv\Scripts folder and report back what files you see in there please? It sounds like the re-install hasn’t worked properly. Do you see a number of files, including pio.exe and platformio.exe at the very least?
If so, then I suspect that after adding the folder above to your PATH, you need to open a new command line session to get the updated %PATH% settings. (Been there, done that! 
)
Cheers,
Norm.