Total *******s

They deactivated my number without my consent or any warning, after calling them they say I need to pay 897 which is for the whole 24 months plus 150 for the new sim card so that I can get my number back because they failed to debit my account with R39 from October last year ,which I wasn't even aware of .They never called to warn me about this ,they decide on themselves that they should just cut you off.My question is why am I paying for the whole 24 months while I owe only 5 months .These people are total *******s as all this was never discussed with me at the beginning of the contract