Account wrong AGAIN

I just upgraded my contract again on 31st march 2015 with Jennifer in Cell C direct and agreed to a new samsung phone with 100 straight up. I agreed to a monthly charge of R135.00pm. Phone was sent on 2nd April.The invoice was wrong and i spoke to jennifer who corrected it by deactivated the blackberry social of R37.00. I have now been told that my payment for the end of april isR189.76. This is totally unacceptable. I complained twice to customer care at cell c but no satisfaction. Gave me ref no ***. Cell C dont come back promptly at all. I told Cell C that if necessary i will lay a charge of ***** against them but they still dont care. I have had a GUTS full of them and if they dont rectiffy immediately they can have their phone back (not opened yet) and i will stop payment at my bank and will be ready to go to my lawyers if needed. Their service is nothing short of Disgusting and i wont allow them to bully me. They had better listen to all the recordings again regarding this upgrade.