With Cell C for 15 years!!!! Calls suddenly go to voicemail when users call me :( DISAPPOINTING!

I've been using my simcard for close to 15 years, but suddenly it goes straight to voicemail when people try to call me. I called Cellc several time and asked them whats going on? they then said i need to take my ID and Proof of residence to the store. But why now? Why cant you give me answers on the phone? This is a BIG inconvenience to me as a student because it ruins everything. I am struggling with almost everything because of this. I refuse to change networks, because i believe incompetence exists everywhere! LOL! TRUESTORY!