Telkom fibre statement

We have a contract with Telkom for unlimited home fibre. We are up to date with the payments, but according to their statement the debit order is insufficient. We were at the Telkom branch in Witbank and it shows on the system that we are up to date with the payments. We tried numerous times to call the billing department, but with no luck. It's frustrating when you have a contract and paid up to date, and then receive statements stating that the debit order is insufficient.