MTN incompetence never ends

I ordered a 20gb plan for R149 pm in June. I received the sim card which has not worked since receipt, I have been to 2 mtn stores at Northgate where I have been sent from pillar to post all the while mtn charging me R195pm. I am now told that I received the wrong deal but no one can help me at the store and they refuse to call the mtn online contact centre because this is not their problem.