Fear the worst and it just happens: Cydia blocked on iPhone.
Apparently, it was reported on Twitter that Three UK, Three Ireland and China Unicom have blocked access to Cydia’s servers. This means there is no way you could fete upon the Cydia repositories, as many folks believed this was a deliberate attempt from the carriers to stop the jailbreaking/pirating.
The good news: it was a “glitch.” Blocking of the Cydia server was not intentional, as it turns out Cydia was put on Three’s adult content blacklist. So, if you are not able to access Cydia on your iPhone, do not be alarmed as it is likely to be resolved very soon.
The issue escalated overnight and the fix came in within a blink of an eye. However, if you are still facing issues while trying to access Cydia, take the fall and contact the customer care to remove the restriction — that is how @Pablo_Diablo from UK was able to unblock Cydia on his phone.
Also, if the “Error: Refreshing Data” message pops up every time you load the Cydia app, simply tap on the “changes” to see if there is an upgrade available. Make the necessary upgrade. If the problem still persists, a fresh reinstall of Cydia should eliminate the issue.