Debit Order

HORRIBLE EXPERIENCE!!

i had a telkom cellphone contract which i was being debited R130 PM which has always been up to date , in DEC 2018 all of a sudden i was debited R709 which i then reversed because i did not understand why the big jump as the contract was prepaid and i have never topped up i tried calling to find out what was happening phone rang with no answer for 10 minutes , in JAN 2019 same amount debited which i reversed again tried making contact no answer again i received a letter of demand this month

and i will not pay for something i don't understand can someone contact me to explain because this continuing will cause unfair blacklisting which i will take up with my lawyer.

i am waiting.