no request for porting a

Someone port my number from cell c to mtn without my concern...i went to cell c at centurion mall on the 12/03 which the consultant assisted me and checking where my number was ported to which was mtn, i then went to the mtn store still in centurion mall to reverse my number back to cell c.. they called their porting department to reverse my number which they did.

Today 13/02 i called the cell c porting department to reactivate my number to cell c..the consultant tells me i need to buy another sim card for them to reactivate my number back to cell c....what i need to know is how so they port my numbers without me requesting it to be port. this is just an inconvinience for me