Billed for water but I am on prepaid, second time this happens in 3 months!!!

I moved into my house in May this year, my electricity and water is prepaid. However in August I was billed for water and sewer, had to take time off work to go the municipality offices to get this sorted and the costs were reversed. Today again when I open my statement for October same thing again happens again I am billed for water and sewer. Now I have to take time off work ang go to the offices as the phoneline *** is going to voicemail. This is very bad customer service and shows incompetence or lack of focus from the accounts department that does the billing, as they are aware that my area the water is prepaid. Please assist as no one reimburses me for the trips and time wasted to go to your offices.