billed while my contract its on prepaid

My contract was converted from open line in to a prepaid in August which my notice was due in October. During November I was billed more than my monthly subscription. Spoke to a lady call Thato(team-leader) she didn't't want to listening to my side off story but rather to force me in believing i was wrong . was told they had system problem as my contract wasn't cancelled. the money that I paid it was for September but funny enough it was debited in November not October. No one is doing follow up on my query . I have to be the one running after you guys..there is no customers service at all.one of the rzn I will never take any contracts with u nor refer anyone to a company like this...ppl are dragging this brand down as a result you guys suck big time.how can one investigation be lodge 3 times with no fedback..I waited 21days and I was told to wait another 7 days..the are other brand if you guys think you the only one. Am glad my contract ended..some staff members need counselling.just because they have ppl reporting to them they think they can also be bossy to customers..