Bad Service

My issues with MTN started when I did an upgrade from 40G TO 80G in Jabulani store, for 40G I paid R401.33 from 15 January to 28 February and I paid R416.78 at the store on the 27th of February for 80G but on the 4th of March R389 was debited from my account whilst I did not ask for the debit order to be done on my account, the guy in the store just asked for the the card that I was going to pay with and I guess he was setting a debit order, I phoned Jabulani store and asked what was the debit order for because I had already payed in the store, the guy said I was mistakenly debited and I can reverse the debit order and I did so the following day, When I checked the bill for March only it was R751, 42, I went to Jabulani to enquire why was the bill for 1 month so high and I was told that it will cover for March and April because I am paying upfront, in the Invoice there was Upfront activation payment for R389 for 27 and 28 February, Pro-rata for R24.16 and R338.26 for 1 March until the 31st, I also phoned their Customer care and I was told that is impossible that the bill can cover for March and April which means the Data only was only for March, on the 15th of March they blocked their data and I can not use it any more until I pay R400.50 that I owe them because they just added R11 on top of R389. Another thing that I want to know is what is the upfront activation payment for because I was using the sim already on the 40G.