Mtn is billing me for a wrong contract package

I went to mtn Vryheid on the 24 December 2015 to upgrade my contract on ***.i took a voice package for the amount of R109 (Blackberry z3 with 25 mins)which was on mtn catalogue by then.On the same day I phoned mtn customer care at night telling them that I see a problem with my package.The consultant advised me that I must go to Vryheid mtn so that I correct the problem.She said fortunate enough the shop is open on the 25 December 2015.I went there as I was advised then the shop was closed then I went back on monday(28/12/2015).I was told that on the computer the package that is reflecting on their system is the one that I upgraded to for R109. I must relax nothing will happen as I was advised by the consultant,but the billing now is no longer R109 as per my selection package.<br> <br> Please correct this mistake as soon as possible.I am happy because you keep call records for referrence.