Note: If the factory reset didn't resolve the issue, consider doing a hard reset, but make sure to back up all the personal data(photos, videos, sounds) before doing the hard reset, because all the data stored on your device will be deleted.
Maybe the SIM card itself is the reason that prevents your device from receiving network signal. To test this, put the SIM card in another mobile device. If the other device is unable to get the network signal, go to the nearest carrier's (operator's) store and replace the SIM card.
If you have exhausted all the options to fix your mobile device and you failed, it's possible that your device has a hardware defect which cannot be repair. If this is the case with your mobile device, consider buying a new one.
Maybe the device itself is unable to receive network signal. To check this, try placing the SIM card in another mobile device. If it "attached" to a network signal, consider taking your device to a repair store.