Poor service from Cell C - 084 140 and Store

After contacting the 084 140 number and speaking to an agent I was informed to go into any Cell C store to blacklist a ****** phone. The consultant told me that I will need to complete a form. Got into my vehicle, drove to a Cell C store, only to be told that they cannot assist me and I need to phone the 084 140 number. Standing in front of the store consultant, I phoned the very same number, and the agent on the other side could not assist me. Actually the impression that I got was that the person did not even know what blacklisting means! I need to urgently get someone to assist me in this regard as the phone is now freely used by a *****.