Billing me what ever you feel like.

I currently have Telkom contract which I pay R349.00 for Hauwei P8. I have 50 minutes which comes with the package. Last month I was billed R394.00 and this month I have been send a stament and I will be billed R653.50. I have never authorized or took an open contract instead if I need more minutes I contact Telkom to give me and I know how much I must be debited. I received a SMS saying my spending limit has been increased to R350 effective from the 1st. I never authorized this and how can I pay so much if I never even ask for so much. I don't want an explanation because with my knowledge I request an amount I need if it not yet month I never request for so much and the always block it when I reach my limit. Please fix your mess and I don't want to be billed something I did not authorize. From R349 to R650 that is crazy.