E-toll cannot close account as they need to refund me R11.00

I no longer reside in South Africa, I have sold my vehicles and property. Upon leaving 6 months ago I return the tags to the satellite office in Rooihuiskraal, which they accepted them. They also confirmed that the account is closed. Six months later I still receive a statement with a balance of R11.00

Please could e-toll cancel my account once and for all. I do not require a refund for R11.00!