Uncapped never same bill

I open a account with Telkom for a uncapped ADSL for R550 pm that was the contract agreement, but never has my debit order been R550 its always more and sometimes I have to pay in extra due to they not debit the full amount, try to call them now that's a joke you call and hold for 40 + minutes just to get the call dropped and I don't have a land line so I pay for all the dropped call I make to them,