Telkom worst service ever !!!!

I have took a contract with telkom for r100 a month for capped data..I spoke to the agent and told the agent that I don't want it to come more than that and capped at that amount ..I've got bills for r900 and most recent bill for r1999 ...I've been calling they call centre ..they keep saying call a different department and that they cannot help us ..they service is absolutely poor ...I really don't know what to do ..Cause they debiting me at any time for the month for all high amounts