Debt-in is a ****

I received a call from debit-in saying my account had been handed over by telkom ..I requested for them to email me the account statement..the account statement showed I owed telkom R150 plus a penalty fee of R200 I asked for the banking details and paid the amount due and emailed them the proof of payment… when I request for a settlement letter I am being told I owe R1318.48 when I asked where do they get that amount they don’t have answers..,this is day light ******* honestly and unacceptable…the staff is unprofessional, phone lines don’t even work when you try to call them