Resetting the BlackBerry to factory settings would not have changed anything with regard to the network. That simply deletes all user data and user settings. If the device was unlocked so it can be used on other networks, it will still be unlocked after resetting to factory.
If the device is blocked because it has been reported stolen, you have a different problem, and it is coincidence if the block happened at the same time as when the device was reset to factory. You will need to talk to the service provider, but I think your odds of straightening it out are not good, if this is the problem.
