That's forgeted up dude. The only logical explanation at this point is that your key has somehow been revoked or the original purchase transaction didn't register correctly.
Unless you try your key on another computer on a different network this cannot be assured. Have you tried downloading and playing Blockland at a friends house or a public library?
Do so when you get the chance, this way we can determine if it's your key that's the problem,
or if it's your own network/PC refusing the connection (which doesn't seem to be the case)