I'm sorry to hear that you're having this issue.
I'm not aware of a way to reverse this.
I'd recommend going to the carrier's repair shop to have them restore your device to the original condition. I'd also recommend saving the contact information (specifically phone numbers and names) prior to having the unit reset to avoid losing important information. It's likely that you can save this to the SIM card, but remove it before having it tested. The carrier's repair shop would likely be able to assist you with that as well.
i accidentally have checked in the reject list the number of my uncle. I did remove his no. from the reject list but to no avail my uncle would still hear a busy tone. Does anyone know how this could be reversed or be totally fixed?..thanks