No Service

I changed banking details on 28/07. This was not done and as a result I incurred about R200 in bank charges for the debit order returning due to insufficient funds on the old acc for 2 months in a row. I had to make alternative payments. 3rd month same thing and now I get messages about non payment. When I address it with collections at ZF Cape Quarter I get arrogant responses about how they're not liable. Of course they should be held liable as this was non service from their side.