Wrong amount being deducted twice

My contract ***) expired on the 11th November. I upgraded on the 19th November. Two months i have been paying a lot more than what i have signed for. I must pay R549 a month, the first month they deducted R704.01 and the last month R715.01. I phoned MTN prelller plein Bloemfontein where i upgraded my contract and they were unable to help me. Today when i visited the store again they could not help me. I phoned head office just for the lady to tell me “i don’t understand what you don’t understand”. Im tired of my money being ****** and there is no explanation. I cant wait for my contract to end so that i can move to vodacom.