Prepaid number disconnected without consent

I have been using my number for the past 11 to 12 yrs, Saturday ( 22 Aug 2015) morning when i woke up my number has been disconnected.A prepaid number disconnected?<br> I visited MTN in newtown junction JHB and i was told that my number belongs to someone else and once validation was performed , then advised to buy new SIM card and don't put airtime nor data bundles cause it may impact SIM swap(old number) process and turnaround time 24hrs, of which am still awaiting with that said I bought a SIM card .<br> My concern: am the one following up on the inconvenience caused by one of MTN Staff member. If my number is really disconnected why am i able to send and receive my whatsapp on that number.I want my old number back.