Hello, have you made an Official IMEI Unlock to your iPhone? If yes, your iPhone should not get re-locked again. Some unlocking services inform their customers that after an upgrade their iPhones might get locked again. If you make an official IMEI Unlock, this should not happen. I suggest to contact the person that unlocked your iPhone first, and then contact with the Mobile Network that locked it (Ask them why they locked it again). This can also happen, if your iPhone is blacklisted! Hope that helped!