Unpaid debit order that tripled without a debit order MANDATE

I have a debit order of R368.60 which returned as unpaid because there was no enough funds in my account, on the 5th of October I received an invoice of R939.40 from telkom, my question is how did my debit jump from R368,60 to R939.50 in a period of 5 days, telkom also tried to deduct the R939.40 from my account on the 16th October without any debit order MANDATE,

I want telkom to respond to two questions 1. How did my monthly debit order jump from R368.60 to R939.40? 2. I want the debit order mandate that allows them to deduct the amount of R939.40