Bad Service by Telkom finance departmentvery useless

Telkom debited my bank acc last month R1551.74 meaning I do not owe them, but yesterday they decided to suspend my account due to a future payment of R1607.00 that is only due on 25 April simply because my acc limit is inssufitient of R20,No communication from the finance department to notify me of this issue so I can adjust my credit limit funny thing they still expect me to pay this amount at the end of this month, I will be cancelling my contract