Overcharged

Well I have two contracts with telkom 1 for data R99 and phone R399 top up deal, which have to be billed R498 monthly from my understanding ..but to my surprise Im billed double. Last month it was R699,70 then this month boom R899,70 like I dnt understand what’s going on!!! Funny part even their poor consultants they failing to give a reasonable explanation . Cnt be complaining every month with the same problem.